Trusted Seller typical process

[aayates]

Newbie question on transactions via trusted sellers. Is it customary to send the seller a watch for trade along with full balance due prior to the seller shipping the sale watch? Or is there a partial hold-back on full payment (maybe 25%) until the watch is received and confirmed? If the former I understand why they're labeled "trusted" sellers. I've done my diligence on the potential seller and he's well liked based on other posts in the who's who section. This is such a big ticket item I wanted to get feedback on the general process for these types of sales. Thanks in advance.