There are a lot of referral postings, however, in most cases it would be better for you to use topcashback <https://tinyurl.com/topcash19> instead! For example, for the British Airways Premium Plus Card you are receiving 45 cash back plus the usual 25,000 Avios! Using a referral like this https://tinyurl.com/caramx18 would give you only 5000 Avios more, so you would be paying 0.90 per Avios! For the normal British Airways it is even worse: topcashback <https://tinyurl.com/topcash19> currently pays £30.00 while you would only get 1000 Avios more via a referral like this https://tinyurl.com/caramx18.
I think many (most?) would be happy effectively paying 0.9p per Avios - especially when you consider that cashback is never guaranteed, but the £30 for the free BA Amex is a superb offer.
If you are signing up to topcashback as a new member, it's worth seeing if any friends are a member - topcashback also pay a referral bonus.
It's a handy site - you can get cashback on a load of different things (e.g. a lot of travel sites). They're currently offering £15 to referrers and £5 to members who join from a referral.