Ugh, I did a standee project at a few grocery stores once, where we had to find them in a backroom that was packed tight enough to make my claustrophobia twinge just thinking about it now. And I have seen that store be fully renovated twice, so it's insane that they still have a storeroom that packed, even if the truck did come in that day. I would never have done that nonsense again, even if my body could still take being on my feet that long anymore. Generally I do far more merchandising and auditing gigs than mystery shopping. I prefer the admin of that work. But only the ones that pay commensurate with the work/travel involved.
One company has been trying to push me, for years, to go to convenience stores and get their managers to order more of a particular product. And my telling them "hell, no" several times doesn't get disseminated between the reps - but neither does, "No, if I cannot be on my feet for more than 10-15 minutes at a time, I obviously cannot do your 8-hour reset." I wouldn't even do those sales-pitch gigs for decent pay, much less crap like $10 a location. If I wanted to be in sales (and I most definitely do not) I'd be in a job with a decent bonus or commissions, not $2 if you convince them to order, on a day when they're probably not planning to put their order in anyway.
Oh, what's that? You'd like me to learn what days my local convenience store chain managers are in, and what hours they are usually planning their weekly orders? Ahh, but that's what an actual route salesperson does, because you are paying them to do so. You're certainly not paying me to do so.