[mninm]

I have no real idea what the ins-and-outs of 1099-K and so I could be completely wrong.

However, it seems like there may be some sort of threshold listed in the reporting requirements.

Would it be legally possible to allow your users to use the enhanced functionality of your platform up to the edge of that threshold?

Cutting off access to the premium services that the sellers of erotic coo-coo clocks (or whatever) have come to value might incentivize them enough to overcome the 1099-K hurdle. You could make the process gentler by constantly displaying the amount of revenue left that they can transact before being cut off.

Be careful though. Cutting off access will equally incentivize users to bypass the restrictions you've put in place by creating multiple accounts, etc.

Lacking the above you could also try to focus on the part of your platform the sellers do want to use and sell a premium tier to sellers that has features that would make them stand out to buyers. For example premium users could have flair (think something akin to a verified checkmark) next to their listings in searches and the ability to post an extra video of their clocks.