The cheaper you buy Facebooks ads for, the less effective they are. e.g $5 ads are good for testing purposes only. If it gets a couple of sales, increase the ad spend. If not, scrap it and try another ad and/or product. You and your friends really need to do a bit of research on how to use FB ads effectively. When used correctly, they are VERY effective. Youtube is the best place to start your search/research.I don't really like FB ads, a couple of my friends prefer not to deal with it as well. It's cheap, but often it doesn't bring any profitable results. .
Any. As long as it has products that are relatively unique, cool and not easily found in local brick and mortar stores. And also has a lot of steady interest from people. (Use Google Trends to check that).please what kind of niche do you think will bring sales.?