i know sometimes its obvious when you're link buillding to tell a drop domain but is there any sure fire way to tell if a site is a drop domain or not?
a drop domain is when someone buys a website domain name that has expired, puts up a new website on that domain name and for a period of time that domain will carry the PR that it had previously until google catchs on and realises that its not what it used to be!
Several services offer dropped or expired domains, but they lose their age when dropped and possibly any PR if they had any. I use dnscoop.com to check the domains age, , check when it was registered as well, when it was renewed, etc. tdnam.com (godaddy.com) and freshdrop.net have low cost domains being auctioned that haven't yet been dropped. There are other auctions, but they tend to be higher in price. If you're buying for the PR check the number of backlinks, but still you can't really be sure.
drop domain can gain PR if we develop it with content and nice interface and dont forgot to get backlink for him too
Have alook at internet archieve, if you see something suspicious like bible study turned into directory then its most likely a dropped domain
As the previous poster stated, looking at the archives can be very helpful. Surprisingly, many of these dropped domains do retain PR, at least for some time (including after toolbar PR updates). Looking at the domain name is a dead giveaway most of the time. If still unsure, I check the anchor text and surrounding text of the backlinks - people usually buy dropped domains because they have at least a few good backlinks and this usually gives it away.