Place like a seapost is a lot of sitting around doing nothing for a lot of days and a lot of hours.

People often wouldn't might making a little extra money to bring home while filling that time with stuff to do.

Could be a drop off point where they will handle it, in exchange for a percentage of the going rate of every item dropped off.

but it would be convenient to get the loot off the ship

Not really. Your ship is already so close, like a 4 step walk off the deck and your already at the npc to sell. Plus you have a harpoon gun (grapple)