I think tracing sumbody on the internet is not easy, what if person does not like to have presence on net????
if you doubt on his background,,then I wud say 1st way is to check his knowledge on the subject,,and rate him whether he'll be able to contribute in your organisation or not,, then approach the organisation where he claims to be worked, and ask about him......
Now there are some more reality,
..some time company does not want to answer your reference check call or mail in detail, coz they think it waste of time as person is no more their asset.
..Or some time his manager whom you'll approach for reference chek could not speak good for some personal reason..
..Or sometime when you'll call for the reference check they will tell you that person has worked with them on certain designation...but probably will not be able to provide the task or work he was handling.....here recruit has chance to manipulate responsibilty handeled.
So in my opinion get the person interviwed by concern depat manager who cud easily assess his comeptency on particular work.
And if person already started working and not able to perform desirable, give him time and coaching both to improve himself..
Eventually our task is to get competent people on the job,,,,judge him from his work,,
reference check is neccessary but some time it fails to explain work nature in detail.he performed..