Go reader CATHERINE WARDROPERgot in touch about hidden extras when hiring a car

I hired a car at Dublin Airport a couple of weeks ago. Online. All very efficient and, I thought, very reasonable. The car was fine, the trip to collect it from the off-site depot was okay – although why the car-hire companies can’t join up and save money by sending one bus every five minutes instead of one bus for each company every five minutes I can’t imagine – but there is a new trick I’d like to warn unsuspecting travellers about.

Usually, one picks up a car with a full tank at the beginning of the hire, then hands it back full at the end. This leads to a bit of driving around at the airport, trying to find a petrol pump, but so be it. The new ploy is to make the hirer pay for a full tank (at an outrageous rate) at the beginning of the hire and hand the car back empty. Of course, I hadn’t read this in the small print (it was there, unsurprisingly). The tankful cost €58.20. I needed only a quarter of a tank. Result: nearly €45 for the rental company – about the same as the cost of the hire. It was a salutary lesson in reading the small print carefully.

JOHN HUGHESof Clonbur, Co Galway, e-mailed about the US government's electronic travel-authorisation system

I would like to add a corollary to Joan Scales’s answer to the question about the Electronic System for Travel Authorization (Go, last week). My wife and I travelled to the US two weeks ago. I had read about its new online system but did not know the fine details. I phoned Shannon Airport and was told to Google “Esta” and fill in the form. I did that and unthinkingly clicked on the first listing. I was asked for a payment of €25 each. Suspicious, I phoned Shannon Airport again, and this time they told me to look for the official US government website.

Eventually, having got the online visa sorted out at no cost, I was amazed to find when we got to Shannon for our flight that at no time were we asked to produce evidence of this visa. Instead, we had to go through the time-consuming ordeal of filling out the long green cards.

Was it all a fruitless exercise?And why can nothing be done about scam Esta websites? Surely it is identity theft, as someone is obtaining names and passport numbers.

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