I see that backlinks.com does not allow the use of the no follow tag, yet google insists paid links should have no follow. Does this mean a lot of sites using backlinks.com get penalized?
Are you planning to buy or sell links there? The problem with them is that they use automated script for link placement, so technically it is easy to catch it unless those who put them on their sites change it a bit so it is harder to detect. I personally use backlinks4u.com and for about a year my sites have not been banned or deindexed.
It's too iffy. Paid links need to be no follow, and besides, search engines will look at relevance between the site you made a backlink on as well as the site linking to yours. Maybe their system works but I have yet to hear from someone who has tried the service and is not an affiliate. Have a good day!
My tip: Never use links services sites (like backlinks.com) without manual link submission option. If you install script or plugin your site is under high risk of penalization