I think Regane is a much better choice over Sea Foam. I used Sea Foam once and it didn't do squat. I always get very noticeable improvements from Regane, and Red Line SL-1 too.
I have only one time had a parts store guy question me about buying additives. I bought a quart of MMO at Autozone last year and the guy behind the counter asked me if I "liked the way that stuff works". I told him that yes, I have been using MMO for a long time, it does a good job and I said something about how MMO helps counteract the negative effects of ethanol in gasoline and improves my MPG. Then he changed gears and made a few comments about how bad ethanol is. Other than that I have never had anyone at a parts store question me about any additives I bought there. If one ever did question me like that, I would just say something like "well, I'll have to try (whatever product it is they are recommending so highly) some time soon". If they still wanted to pitch the product or try to argue with me about it I would just make an excuse to go back out to my truck, leave whatever it was I had planned on buying on their counter and go buy it some place else.
I know what products I like and I know what works well in my truck. There are too many other stores around here that all sell the same items to put up with the "parts store experts" who want to push you into buying one product or another or disparage a product that you want to buy. It's very unprofessional. I guess the store must get a perk or a bonus for selling x amount of one product or another in a given month, so they try to pimp it out any way they can.