I would recommend mordrag_05 if you are looking for NA West account who I believe was selling items from his Vella account and he is also trying to sell the entire account too so go check it out if you are interested. He is very trustworthy and also a West gold seller that I always buy from and put my absolute trust on .
To answer the buying gold question, no you won't get ban since it is not a breach of Terms of Service if someone sends you gold there is no way to ban someone just because they receive gold from someone else via mailbox or MP assuming that the person giving you the gold did not earn it by illegal means such as botting. But since botting is not really possible atm everyone that is selling gold earned it legitimately.
Well first of all confirm that the one your doing transaction with is really them by asking them to send a Visitor message on mpgh and vice versa. Also using an Official Middle Man is the safest otherwise, if the seller has a lot of vouches, you should go first by sending money via paypal to the seller, then he will confirm it and you then either COD some random item(like a cloth or something lol) to him or list an item in the MP for the amount of gold you bought and the seller will buy the item from you and then transaction would be done and you vouch for him on the forums. If the seller doesn't have any vouches at all, it is safer to use a middle man or if he is willing, ask the seller to go first.