Yes, we have a black list for websites/domains that we deem inappropriate for Buxr. It is usually not for retailers but some retailers do manage to get there. One example is iHerb. We think it is a legitimate site but we got swamped with $5 off first order coupons and eventually decided to blacklist the domain.
If a merchant is in the black list then this is exactly what the message will say. We are having intermittent problems with certain merchants (newegg is an example). Something related to IPv6. Just retry again in a while, this is the only way around this for now until I find time to look more closely at what is causing the error.
It is both really. Some are legitimate companies that we consider low value (say if they only accept Paypal and don't have a normal merchant account for credit card processing) others are deemed scam. There could be other reasons why a website gets blacklisted. iHerb (the example I gave above) got there thanks to their aggressive referral program.