I have ads on Spider Sales and am getting traffic, however I do not see links from my ads on that site that show as backlinks for my site, Having said that I am considering deleting the ads that are not giving me traffic, however if I could tell if these backlinks are working I might keep them just for the backlink benefit. The ads have to be gown though and the end date must be changed so if I do delete some I will not have to teak the time to renew.