Not if Occam's razor (plus centuries of actual experience with catching fences -"professional" buyers of stolen goods- in such the black markets) simply puts the profit motive as the most possible explanation.

It's as if people never heard of art and jewellery heists before...

Are you saying the buyers and sellers don't cooperate?

Are we expected to believe that high-value buyers wouldn't authenticate the art they buy?

I'm saying that cooperation between buyers and sellers is something that goes on since time immemorial not some big conspiracy with unknown motivations...