Very positive results with GunBroker. I always contact the seller and have any questions answered and issues resolved before bidding. I will only pay by credit card, or US Post Office Money order. I've had two sellers insist on me wiring the money to them. That always raises a red flag to me; I won't do it. Bill.
I have bought many things on GB. Only thing I have to add to the rest of the advice is a golden rule of mine - if no inspection period is allowed, move on. Most sellers who are reputable will offer an inspection period