What should it never do?
Distrust these, from any provider:
- Promising rankings, a position or a date. Nobody controls those.
- Selling a fixed number of links without looking at your site first.
- Hiding where links are placed, or refusing to show example hosts.
- Using networks of blogs built only to sell links, often called private blog networks. Pages that exist to pass links are what Google's link scheme policies are aimed at.
- Pushing exact-match anchors on every link.
- Delivering links in one large burst instead of a steady pace.
- Asking for payment before the scope and quote are explained.
A provider that does any of these is spending your client's reputation to save its own time.

