My experience has been different than Jim's. I can't remember ever getting one that did NOT have oil. This really is a problem these days, because you don't always know if it has the right kind of oil.
He needs to open the ports, turn the compressor by hand and get out all that he can. Then put some of the oil type he wishes to use in and use it to flush the compressor as thoroughly as possible, then empty as much of that as he can get out.
Then install the compressor into it's brackets and pour in the specified quantity of the desired oil. Then connect all the hoses everywhere and turn the compressor by hand several turns to get a little of the liquid load out of the compressor.
If he does a lot of a/c work, I'm surprised that he does not know to do this. It also makes me wonder if he knows how thoroughly he needs to flush the system after a compressor failure. If there is junk left in the system by not flushing thoroughly, the new compressor will be ruined in short order. If you are replacing the compressor because the seal was leaking then there shouldn't be too contamination to worry about. In that case, he will only have to flush if he is changing refrigerant types.