Hi..
I dont know why Organizations follow the procedure of ref check after giving the offer letter..imagine, all the wastage of time and money when after finishing all the procedure you get to know he or she is fake.. I have seen diff trends among companies..some do ref check, before HR Round..some do ref check after deciding upon what all candidates have to shortlisted, i.e, before giving them the offer letter..and also some do it later on..
But prevention is better than cure..The procedure i follow in my company is.. though employees already provide their ref no., but i hardly use that..i try to get the contact details of his company on my own..and randomly call up to know abt him..coz the phone no., he will give in all probabilities would have done a prior setting..so in order to avoid that i use no. taken from wesbite or directory..thats a fool proof check...before me, in our company we had outsouced this work to agencies..which used to do a strict background as well as professional check..
so..its ur call now!!