One of the bizarre tenets of many D&D campaign worlds is that the Thieves Guild is a legitimate government-sanctioned institution. Furthermore, performing non-Guild-sanctioned robbery is likely to get you in trouble.
This puts the Thieves Guild in an interesting position regarding your stolen property: either they stole it (in which case they know where it is) or they didn’t (in which case they’re interested in hunting down the freelance thief.) Either way, they’ll probably be able to return you your stuff, for the right price.
The Thieves Guild might easily develop into a legitimate stolen-property detective force open to the public.
Being part of the Thieves Guild Detective Agency might be a decent job for PCs – even good-aligned ones. You get to rob from robbers and rough up ruffians. You can mix bad-guy heists with good-guy heist investigations.
If, on the other hand, there’s a murder investigation? That’s a case for the Assassins Guild.