Generally, if you’re a professional reseller, the worst possible place from which you can source your products is from, you guessed it, another professional reseller. It’s nothing personal, but the reality is that flea market vendors typically price their items stiffly, and often have a large accumulation of low-quality products.
The danger, of course, is not that you will accidentally buy some low-end flea market stuff. The risk is that you may suspect that some items might have resale value and waste your time looking into them. You need to save your time by quickly identifying a sale that is unfriendly to your business and moving on to more productive sales.