So, I have kind of a crazy idea, it might be totally far-fetched.
1. Disallow sale of player-made clothing and art to the markets.
2. Open Ashlin Pawn as a consignment shop where players can sell player-made clothing and art and specify the price. It would be like C&C where everyone in the system has a number.
3. If no one buys the item after 2 weeks, it gets removed from the game and the seller gets a tiny token payout. This would incentivize the seller to price fairly aggressively.
Doing something like that might help players self-select the custom clothes that should stay in the game (because they're worth something to someone) and would give robbed people a chance to easily find and buy their threads back. Having the numeric tracking system like C&C might help people figure out who is selling their stuff.
As for this bypassing regular fixers, my own feeling is that it won't; people will still take player-made clothing to fixers for the guaranteed payout (if anyone is interested) and will turn to the consignment situation afterwards as a kind of last resort. Because you won't be able to sell player made clothing at the markets, it will all eventually get funneled to the consignment shop (unused stuff) and deleted if it's not sold.