Not sure who posted about having a minimum threshold, but that's the same for me, albeit a little lower - Anything worth less than $20 is just not worth my time.
I also don't bother to respond to anyone that can't form a complete sentence. It has drastically cut down my issues for the most part, outside of the people who want to try to haggle me when they get there. I usually like to respond to the last text when we confirm a meeting with the price, I've weeded out a few people that way as well.
The new review system is pretty shitty though. I wish it was setup like "eBay Local": People bid on my shit and I deliver it to their door, lol. That way my only dealing with the Kijidiots is the final step.