1. In my experience, this sells best on third world countries where saving some dollars on the price is really meaningful. In first world countries 5 or 10$ is so little that people won't bother buying your accounts, they will just go official.
I am from South America, and it works in every country here. I also did business as a provider with people from ASIA (indonesia, malaysia), and people from Africa.
2. Well thats the hard part of the business. Since you cannot promote it because ADS get banned, getting customers is hard. Most common thing for sellers is to start with family/friends, facebook groups, local forums from your country etc. Word of mouth will take you somewhere.
In this business you need to be creative to promote. Find local FB groups where you can buy a pinned message, buy stories. Find a way to avoid FB and IG ads bans.
3. If you have any other questions I can help with let me know