So many of the websites raised red flags that I just stopped looking.
I favor provenance, but my primary interest is ancient provenance.
Authenticity of course, but I find coinage of obscure satraps with brief reigns interesting just because they nail down a small geography and time period, as opposed to say an Alexander the Great coin which, who knows, there were a ton of them everywhere.
Only time I've directly purchased coinage was for the purposes of melting down into a ring for my now-wife, and that had provenance paperwork just to ensure I wasn't enriching modern looters.