We have used masterkings at Faro airport for the past few years and have been very satisfied with their service until our recent trip. I will agree however that even on previous trips you have to follow up to get your toll transponder deposit back, I assume most don’t and this provides some extra income. However we recently were charged almost 50 euros when returning the car due to a bit of sand, we have never had an issue with this before and it wasn’t that bad, I assumed that the cars are usually wiped down before a new driver anyway. I asked if they had a dust pan and brush to quickly do it myself which they didn’t, so I tried the local service station but unfortunately the vacuum was out of order, I was told there was another service station a few miles away but I couldn’t find it and we didn’t want to miss our flight, especially as we had our 2 year old with us. So if you do use them beware of the extra charges, they still might work out good value but we will be shopping around a bit next time.