I keep seeing people complain about liquidity at Fairlay but every time I check it out myself, I can see some pretty big orders there, for sure more than 1 BTC for even the lines I bet,,, I do not think there are that many whales who go for exchanges!
Keep promoting them and they will grow, just like OP says, Betfair took a long time to become popular and that is with fiat which almost everyone could use.
I don't know what liquidity is like there, but the website is a nightmare to look at, let alone use. They have some very odd features and a lot of tech issues historically around bet matching errors. But they seem to be honest and doing their best, and that is to their credit.
I am not looking to 'promote' any product.. If the product is good and provides me with value opportunities, I will be a user.
I am amazed the BTC space doesn't yet have a dedicated betting exchange that is built to professional standards.