I am hesitant about using mass back linking services. Will Google know that these back links were bought... because of the amount accumulated all of sudden?
so is it safe to say getting 20-30 at a time is safe than getting a few thousand for a link service...
That sounds like a really low figure. From what i've heard, Google would probably consider getting 1000 backlinks in one day for a brand new site to be excessive. But for a more established site, it might not at all be unusual for 1000 sites to voluntarily backlink to a particular site. As i'm sure that's the situation with many popular sites like Facebook/Youtube/Coca-Cola, etc.