Answers to a couple of questions...
1) must have, and if necessary use Visa DEBIT card only
2) the "trigger" is the usage of that debit card in a way that will cause the surcharge for using it... Some establishments will add 3% extra if you use a debit card........ Some establishments will charge you extra if you don't spend a certain minimum amount. In that case, you spend less than the minimum to "trigger" the fee.
I have done couple, and would have done more but I waited too late and locations became unavailable. I am comfortable in almost any setting or situation, so for most of the assignments I don't have a problem walking in and walking out without a purchase. By the way, those are the quickest, the no purchase shops. However, you never know which one will require a purchase or not. You only purchase something if there is confirmation that there is a surcharge for using a debit card. If there is signage, you are required to take a picture of all signage that indicates a surcharge. Typically, that signage will be at the counter next to the register. WARNING.... what the guidelines don't mention, at least I haven't seen it, is that you need to take a picture of the counter where the register is located at all locations, debit surcharge or not. I learned that doing the evaluation. Some situations could be awkward, and nearly impossible to covertly snap pictures of counters and signs. For example, one location was for a barber shop. What the heck! I don't mind going in and walking out without getting a cut, but I don't want to try to covertly take pictures of the counter/register in a little establishment like that. Furthermore, $5 haircuts died in the 1960's. I prefer markets and restaurants. I just look at the menu in the restaurant and leave, or get a bite or drink if there is a surcharge. The visitation is usually 1 to 3 minutes, and the evaluation takes about 5 minutes.