You need specialized software and hardware to mine, or you have to rent hashpower... Seems only natural that markets are popping up and people are buying/selling. A simple web search for buy bitcoin testnet coins or something like that reveals places that are selling testnet coins, and they are very cheap, probably just meant for devs who need them and to dissuade free loaders from hoarding like they do on faucets. Testnet hasn't been reset in ages, not sure if it ever will be at this point, but people are going to speculate on anything especially when in demand and limited in amount. I say just spend the few bucks for tesetnet if you need it, at least you aren't buying altcoins!
1. I believe 0.012 tBTC is enough for many kind of testing.
2. The tBTC seller probably care who buy their tBTC or reason for buying their tBTC.
3. While it's trust we haven't see testnet reset in very long time, both Signet and Regtest also exist.