The ahrefs tip is underrated, been doing the same thing for years. One thing i'd add to the traffic check though... dont just look at raw numbers, look at the trend over the last 6 months. A program thats slowly bleeding organic but still pushing aggressive payouts is usually robbing peter to pay paul, new affiliate money covering old affiliate payouts. Seen that pattern a few times and it never ends well.
Also
@amenhot the third party review thing is good advice but take fresh review sites with a grain of salt. Half the "reviews" out there are either the program owner astroturfing their own thing or competitors trashing it. I tend to trust forum threads with actual post history behind the accounts more than some standalone review domain that popped up last year.