The risk is a new member could be anyone. Unfortunately this hobby attracts a lot of scammers who count on the chance of the scammed people not going to the police to tell they buy/sell counterfeit goods. Since we're relatively good here in identifying scammers and ban them, new accounts are constantly made from these lowlife to take another chance, so, new members are more likely to be scammers than old ones.
Apart from that new members often have unrealistic expectations about replicas and a perfectly good rep could be questioned by the noob buyer, bringing a lot of hassle to the seller. Or even before buying, some new members tend to have a lot of requests and need a lot of explanations while experienced ones know what they're buying. This is sad maybe but it's true that if I can choose, I choose to sell to a long-standing member. Some people even ask you what movement is inside a watch, is it any good, how does it compare to other factories. Sorry but that's not my job to tell a prospective buyer, I don't do this as a profession. An experienced member will pm you "if it's not reserved yet I take it" and be done with it.