Sites like that have existed for a while, at the end of the day you need to bring your products and quality to a level where you can clearly articulate what they’ll get for $30 and what they’ll get for $3000 - at that point it’s up to them.
If they just needed any kind of crapped together graphics for his THC-infused bubble gum cardboard POP stand, then just walk away. He’ll probably realize that he’s not going to get what he actually wants out of it in a few weeks and either come back, or be happy with the crap he got.
We had someone at my current job pay a “fiver” $180 for a character design. That person took a $3 CAD model off turbo squid, added an extruded letter to it, and sent over the rendering. So for them, $180 for ~30 minutes of production work and emails was a great deal. The client didn’t know that it was just a stock 3D model so they were thrilled.
At the end of the day you just need to walk away from those clients and try to find clients with pockets deep enough and reputations important enough they don’t want to screw their creative work up.