Barter on the flea market is only possible with found in raid items.

Do barters count as found in raid?

if you barter only found in raid item with dealers (not buying from flea) the bartered item should also be found in raid. for example, if you find all the items needed for a SICC case barter you should be able to sell it on the flea.

What counts as found in raid?

An item is marked as "Item found in raid" if: it was found in a raid, was not brought into that raid by a PMC and extraction status Survived (and not Run Through *). it was crafted in the Hideout. it was obtained as a quest reward.