I get the sentiment here, but, at least in the case of AMP providers, that would concern me. It makes me think of a situation I had at an amp. I gave the $$$$ donation up front. When I put down an extra $40 tip at the end, the girl looked quizzically at it, and then said I owe her $$$$ not 40. I told her that I gave it to her at the beginning. She insisted that I never did. The MMS came in and seemed disposed to take the girl's side (which I didn't totally fault since she knew the girl and her character better than she knew me). A couple of minutes into the dispute, I noticed an envelope on a dresser and told her to look there. The girl opens it, and there are the Benjamins I gave her. She had put the money in the envelope but forgot, and she apologized profusely. I'm a calm guy and never let it escalate. But I can imagine that kind of situation becoming more heated, the girl pulling a gun to demand what she believes she is owed, and accidentally taking off half of some innocent guy's face.