Had so many thoughts to get out, and was running out of time.
Forgot to mention LocalBitcoins, Paxful, Wall of coins and similar.
With those sites, you are basically choosing them as the arbitrator. Except they have they keys, and you get to pretend you have the keys. You are mainly either trading Fiat or a gift cards priced in Fiat and altcoins (with BTC escrowed). On those sites. You could trade products on those platforms, but it's not their intended purpose. Use the right tool for the job.
They offer some protection, and are better than exchanges like Gemini and gdax in that they only hold your BTC, not your Fiat. But you do need to watch who you trade with, especially selling.