Being a developer I have the innate urge to try and replicate whenever I encounter a crash in a game. In this case I was busy trading with the caravan merchant who walks between the Mojave Outpost and the Lake.

Details:

After having selected my stuff to sell and his stuff to buy, pressing accept would consistently crash my game.
Going to the Barracks to trade with Lacey would work without any problems.
Going back to the caravan merchant outside (they were sleeping in their outside fenced area) to buy some things (so no selling at all) I found that after selecting my goods it would still crash.
I then proceeded by buying in batches: 1 item, 2 items, 3 items, and so on, making sure to press accept after each batch that I selected.
Sure enough, a batch of 4 items selected (or more) caused a crash.

Sadly enough, on my 15th, or so, test of this I also managed to crash it buying 3 items.
After that I managed to get through with buying in batches of 1 item only to crash trying to save my game after exiting the dialogue.

This is not so random since it constantly involves this NPC, so something must be weird at this point with this NPC and his inventory. Too bad the batches of 4+ theory didn't hold, would've made things much easier. My gamestate is pre-Novac.