Is is worth to keep promoting Namecheap, Namesilo?

I have made like 10 sales for Namecheap. I did not read the the TOS carefully. Actually, they only pay 1 time. "Affiliate commission is credited only for the first order of a new user ". That's not fairly at all. I personally have spent hundreds of dollars on domain. With that program who has motivation to promote theme?. Are anyone here still promoting them?.

This is probably a topic for the affiliate forum (https://www.blackhatworld.com/forums/affiliate-programs.15/).

In my experience, there's good money to be made from "new user only" affiliate deals IF your marketing strategy attracts the right kind of people. For example, if you attract people to content on "how to create your first website", you'll do great. However, not all domain-buying content will work.

I recommend diversifying your affiliate offers, and using Namecheap in combination with other programs. This offers your market choice, and also increases the chances of getting a commission from somewhere.