If he's got the green slip you'll be fine.he sounds genuine enough as he's obviously sent the logbook off himself and you've done the usual checks I can't see really where you can go wrong.again phone the Dvla and it is correct that you need full logbook number and chassis to get their guarantee.Get a full written reciept where you BOTH sign it and if poss get it witnessed.if the guys genuine then he won't mind but explain that you've been caught before,just helps lighten the situation a bit.