I agree with SEOMonster01 that the pattern itself is the warning sign, because a site that was available when you were only asking questions rarely becomes unavailable at the exact moment you are ready to pay. That timing is what separates a genuine change from a bait and switch. What I would add to the checks already mentioned is to look at the site as a reader would before any money changes hands. I check whether recent posts are spread over time and cover the same topic properly, rather than a run of unrelated guest posts published on the same day, because that usually tells me more than a traffic screenshot. A working contact or submissions page helps, as SEOMonster01 said, but I also look for a recent post on that exact site that is still live and indexed, and I note its date myself instead of trusting a screenshot. I also agree with toastymug about keeping everything in chat. The agreement should name the exact site, the final price, and the rule that no substitute site can be used without approval, with a clear exit if the agreed site is not available. That way a last minute swap is a broken agreement, not a negotiation. After publication I would still check the post myself a few days later, as c.sofia suggested vetting matters at every stage, to confirm it is still live on the agreed site and has not been changed or removed. Starting small, as bravis said, also limits the loss while you learn whether a contact is reliable.