I can highly recommend My Art Broker if you decide to invest in art, especially Banksy prints. I have bought (and sold) several works by Banksy through them over the past 5 years including, recently, a signed Love Rat. Their service is excellent and I haven't had any problems with payment (in either direction) or receipt of PEST certificates. All the prints were in mint condition as promised and in my experience you can buy (and sell) with absolute confidence. I will definitely be using them again in the future.
I have recently purchased a Banksy piece through Joe @ myartbroker and he was superb! He dealt with all of my questions and queries in a professional manner, I would not hesitate in recommending Joe @ myartbroker to anyone who was thinking of purchasing a piece from them in the near future. Thanks again Joe!