MD - I haven't read all the responses here and I'm probably going to repeat a lot of things you've already heard. I'm sorry for that, maybe it will give weight to some suggestions, possibly I have something different to day but let me tell you, I wish I could you a big bear hug for all the pain you're going through. You sound like a good guy and much better than she deserves.
Your wife, I hate to say it, but she sounds like a pretty garden variety cheater to me. I would not be surprised if this was not the first time. You probably have already thought this. I would. She seems,even from your description, like someone who likes the attention and fawning she gets, maybe she's insecure, maybe it's narcissism, maybe she's restless with her life, maybe it's something else, but this is not a one time thing - I don't mean the affair, I mean her attitude and need for this kind of "admiration" or attention, whatever one calls it. It doesn't seem to be a sexual need as he is unattractive as you say - THAT IS OFTEN THE CASE!!!! You would be surprised. At some level, it's any port in a storm. There's a whole thread on this site about how they affair down. And they often do, because a lot of it is about being praised, feeling special, feeling desired, wanting something new...etc. These, to me, are personality defects, not just behavior to a specific event. Yes, this guy should be fired IMMEDIATELY but it's not necessarily easy (as a former manager I know) you have to go through a process and it can be a lengthy and detailed one. It might also be that the management structure there is also sleazy so this might not be that big a thing to them, but it CAN be hard to fire or even discipline someone unless you have multiple complaints. I think you may have to get your items in a different way - is there anyone else who can purchase these items over there? She's caused you and the family business a lot of problems with this - potential financial problems and loss of business in a hard economic time and THIS SHOULD BE EMPHASIZED TO HER. There are CONSEQUENCES to this behavior, not just with your marriage, but with your financial life and security. This can't just be shoved under a RUG. which is what she's trying to do.
What she's done is typical. It's called love bombing to try to reassure you this meant nothing, just go back to sleep and forget about it. When that does't work it goes to rug sweeping, and then anger when you insist on knowing what the hell happened and setting boundaries. You're requiring her to be accountable and she just wants to rug sweep and pretend it didn't happen.
You can't do this. Obviously. This has severe emotional implications in ANY relationship...and it potentially has severe financial implication as well. This is not like denting the car. This is crashing the marriage. It's serious. To me, my main feeling about cheating, esp in a long term relationship - which took ME by great surprise when my husband did it - was....I never saw this coming, I never thought he could be "that kind of person". I saw a whole side of him I'd never seen before. That was the most disturbing thing because I wondered....well, what else was there? What else could he do? WHat could he do in the future? You realize that you don't really know the person you thought you knew best in the world. I always prided myself on my judgment in people. You can imagine where that went. So....bottom line....you don't really know your wife anymore. To the extent you need polygraph tests and to recover messages. And you are NOT overreacting....you don't know your wife anymore. And she's not helping you to get to re-know her or learn about this side of her and how to handle it - if you want to.
It is HER responsibility to help you to feel secure, comfortable and trusting of her again by revealing everything about her that you don't know. Making you feel like she is a safe person again, that you can trust and whose behavior you can predict, including in a BUSINESS. She sounds very immature.
I think you're proceeding in the right way with the poly - which she might pass too, people do, even liars. I would pursue getting the recovered messages if you can. Even if it costs quite a bit....you need to know who you are married to and what she is really like....now....and what she is capable of. If you can't re-establish that base line and she's not helping you, how can you marriage continue and certainly improve? She needs to work with you to re-establish your sense of who and what she is and what she is capable of.
Also....this young man was not a predator. He was an opportunist as many young men are. Your wife may have actively been flirting with him, you don't know. She was as much a participant in this as he was. If a young man kept coming on to me like that and I was not interested, I'd ignore him, let him know, tell him I'd tell my husband, or tell the store manager, or not go back there or something like that or a combination. I wouldn't keep going and let this happen. When I've had men come on to me or I could feel the potential, even now because I'm not unattractive even at my age....I try to defuse it or not be involved or cut out the conversation, etc. I don't let it continue. She is AS RESPONSIBLE FOR THIS AS HE IS. More, I think because she is the older person and she is married and she is doing this in front of her children. Obviously none of his is acceptable. Don't let her play the victim with you, nor assume she is one. She isn't. She's a participant.
I think she has to start realizing the damage she has done to you personally, to your marriage, to your business situation, possibly to your children as they wonder what the hell happened, and that SHE HAS TO TAKE RESPONSIBILITY FOR THIS AND TRY TO MAKE IT RIGHT. SHE has to do this! This is HER responsibility to change and correct and show you she's not going to do this again...or if she has some kind of issue or problem that is ongoing and like to recur....SHE NEEDS TO FIX IT. You can't. You can't fix someone else.
This is not YOUR fault....If she hasn't already....she might start blaming YOU because that's a typical part of this behavior and DO NOT ACCEPT ANY OF THAT. This is HER FAULT. It's not your fault, and it's not the clerk's fault, frankly. It's HER fault. She needs to come clean and she needs to change and she needs to reassure you and let you know clearly and accurately who she is and what she will be.
I'm sure people here have had many suggestions for you and hopefully resources you can use. I would continue with the poly and do try to get those messages if you can. I'd talk to an Iphone expert if you can or maybe a PI. I know it's money but....it's your future and your kids' future too, I think it's worth it. You have to KNOW what you're dealing with or doubt will wreck everything anyway. Doubt doesn't just go away, you need real information, corroboration and confidence.
Good luck!!!