just arrived back from Istanbul last night and was lucky to make my flight as Sun Rent A Car didn't turn up (despite numerous calls to remind them, met with lies about the driver being delayed by '5 mins' then 'another 5 mins'). Eventually (almost 45 mins later) I hailed a yellow taxi (40 TL as opposed to the £80 (yes, 80 Pounds Sterling) return price I'd paid for Sun). They lied about the distance to Sultanahmet from the airport, used various scare tactics (like taxis will take you the long way round), waiting hours for shuttle buses etc until I relented and booked with them but the return trip wasn't worth the paper it was written on. Once I checked in last night I went back to their office and demanded my money back - of which they (reluctantly) gave me Euros 50. I guess the moral of the story is not to pay in advance for anything, but Sun were determined to sell a return journey ... and now I know why! My suggestion is (a) book taxis through your hotel or (b) take a yellow taxi - you can either go on the meter or agree on a price before getting in (several times I was quoted (eg) 'about TL 10 to TL 15' and once you're in, it's suddenly 'about TL 20 or TL 25'. (PS I'd never heard of this website before and have specifically registered just to say my piece about Sun Rent A Car - they're thieves).