> Couldn't these be tracked technically?

There’s no KYC when you give someone cash so there’s no KYC info attached to these serial numbers.

Don't $100 bills have serial numbers? Couldn't these be tracked technically? 

Also you run the risk of the deal going sour/getting robbed, right? There is a lot of trust being involved with a stranger here. 

SatsMate

DrStacker

How is it "no KYC" if you are paying with electronic fiat? You would have to do a cash trade in person for it to be "no KYC".