I decide what I'm paying for and I always want to at least see the gear , if I don't like what I see I don't buy. I always carry scales to check weights or ask them to weigh it out in front of me (I check thier scales by placing a coin on them that I know the weight of). If I was buying large amounts I would expect to be able to try before I buy.
I don't fuck people around and I get a little bit agitated if people try it with me.