In terms of "SP’s asking for money advances in the promise of future sessions", I've only done this once. An SP who was looking for money on a deposit on a new place, so she put a "prepay with a discount" offer on Twitter that I arranged over DMs and finalized with ETransfer. She was someone I hadn't seen but I was following on Twitter for a while, she is established (worked in both agencies and independently, history of Twitter use and unique pictures, history of reviews), she is pretty, and the date was fun (I ended up missing one of my favourite parts of a date, but she help unlocked another fetish of mine in return that I didn't even know I had, so good date overall).
I have prepaid 2 other SPs who I've seen multiple times and trust (though these prepays I asked ahead of time on my own instead of the SP asking), and already had one of those amazing dates, and I'm still trying to figure out time for the last date (school and covid are a pain to work around).