I got a pair of pirate pants cursed with -3 life regen. When I went to sell them, it gave a price of -23. I dropped em on the table, and Drax offered to sell them back to me for -113.
Then exploit Drax in that piratey way. I wouldn't want to buy cursed pants, though. But honestly, it does seem weird as one would expect the lowest possible price to be either 0 or 1, and negative price is kind of exploitable (not that it matters that much, as there are already ways to get infinite gold, and it's not like you can get everything with it).
Wait... brax sells stuff back to you when you sell him stuff? I have never seen or heard of this before.
Apparently you can sell something by placing it on the item pedestal in his shop, it will stay there and you can then buy it back.. I haven't tried it, but I heard the Devs say it on their interview on rogue-like radio.
Cool! I learn new stuff daily! Of course, why you would do that, unless it were purely for the 'loan' is beyond me.