And another one: if the earnings are good, but the free cash flow stays negative, you might be up against some foul play. It may be nothing more than a period of heavy investing, but the last time I saw this, it ended up with the owners buying out the company.

This might seem obvious, but stay away if the auditor says anything equal to "Meh, I don't know if this is legit or not". I have seen that in a few reports.