So you accepted a quote over the phone and now your complaining that he finished the job quicker than he thought. I think he was been very reasonable in only charging 2 hours in the first place. Suppose the job was trickier than he thought and took 3-4 hours would you be paying him for actual time spent working? It cant work both ways
From a tax perspective, how can getting a receipt help ? The last receipt I got from a tradesman was from a receipt book you could buy in any office supplies shop. I could have written it myself......and always get a receipt - don't let these guys off with a 'cash' job