Transfer Ownership of Vechicle, Seller is not Staying in Qatar, But has a Valid RP

You have a few options:
1- seller goes to Qatar Embassy wherever he is and signs a power of attorney authorizing you or someone else present in Qatar to commence the sale of his vehicle. He will need a copy of his passport, a copy of the car ownership papers and a copy of ID/passport/RP of the guy he is giving this power of attorney to.

2- You go to a car showroom and you argue your case, but at least you must have original ID of the owner of the car. It is very unlikely that they will help, but a car showroom can stamp a sales document which means they have seen the buyer and the seller. again, original ID is a must or passport of the seller.

3- You get the seller to write you a paper (contract) and sign it and you go argue your case at Traffic Police department. Make sure you go to the commanding officer and not to the guys behind the counters. they have no authority on this matter. Again, chances are low but you will never know until you try.

I hope you did not give the guy the money :-)

Alternatively, you can drive it forever because you can renew the permit of the car anytime you want without the owner present. however, you will not be able to sell it to someone else.

good luck.