Hello to all,
There was an archived thread about that withotu real answer :https://forums.beamdog.com/discussion/6696/selling-stolen-items-in-bg1
Finally I managed to find a merchant that accept stolen goods
You must go to Durlag's Tower (far east of Beregost) and at the top left corner or the map there is a thief asking what can he do for you, you can chose any reply he will open his shop anyway, and you can sell all items you want including stolen ones.
Name of the NPC is Erdan CRE name : ERDANE.
Note that you cannot steal him, so no steal/sell glitch as in BG2.
He also sell good throwing weapons like 400 acid arrows and 200 stun darts for example.
You can summon him with the standard console command as there is no script attached (only first dialog) :
Have fun !