My definate check would be the "hot/cold" check-if buying or offered a geniune Rolex then in addition to asking for the back removal another check would be the cold/hot look- what you look for is condensation within the glass face when watch plunged from hot into cold water or vice visa-a gen Roller would be vacumed sealed with all air drawn from the watch internals consequently no condensation should take place-many years ago i had an old GMT mk 1 c1975, had it seviced by it being sent to Bexley,Kent as being the official Rolex sevicing factory(cost at that time £39.50 through Northern Goldsmiths,Newcastle)the watch returned like new-fast forward to next service and I hiccuped at £125 cost-
on going through Exchange & Mart there was a guy who claimed he had beeen employed at the Bexley Factory and could do the servicing cheaper- in my naivity i duly sent the watch to him (cost then was £49)-
on receiving my watch back I duly went swimming on a cold winters day and wearing my newly seviced timepiece-low and behold condensation clouded the face-it was returned to the servicing guy for rectification duly carried out but at a loss to the chap who serviced my watch and with the explaination that all Rolexs are vacum sealed and by breaking the seal the vacum is compromised and has to have all air drawn from the watch innards before sealing on screwdown-
so that is a test in my view that may give an indication of the offered "Roller" being what is claimed by the seller-
buyer beware!!-if you are prepared to be screwed, you will be!!-told to me by a horse trader!!