I must admit I do tend to ignore advertising approaches made from gmail accounts. Perhaps I am just paranoid!
Realistically there are probably some patterns/systems by which they look out for non-natural links. And there are likely to be many sites that are blacklisted for being very blatant (and high volume). But most of the rest is going to go unnoticed. Quality/Relevant in-content links (at a low volume) are probably the best way to go.