hmm they do and thats why we always book our car through the ba website when we book our flight. previous experience was that you paid what you thought was it and then they tried to sting us at the desk after a long tiring flight when we had no energy to argue. they try and add on collison damage waiver extras, car seats, insurances for second driver, sat nav, toll booth sensors the lot. also try to get you to sign up for them to fill it with petrol when you return it at double/triple the cost per gallon. be v v wary and get their terms and conditions in writing before booking.
Funnily, I was going to suggest Avis booked through BA. No extras, spouses included as drivers at no extra charge, flexible pick up locations (we wanted a local rather than airport collection, but airport drop-off). And the rates are cheaper than any of the discounted ones.
Buy a sat-nav and carseats on arrival at the nearest Wal-mart.
Do not, I repeat DO NOT use Budget!!! We used them recently because they appeared to be the cheapest. We paid in advance so that we knew we were all sorted only for my husband to be given paperwork at the airport saying on car return we would be charged $400 plus $40 to fill the fuel tank. My husband questioned this and made it clear that he didn't want any extras, just what we had booked and paid for. The man at the desk said it was an error as we had already paid. My husband signed to agree to pay the $40 for fuel. On returning the car he wasn't asked for the fuel money so he asked the staff about it and they told him it was automatically charged to his credit card. When we got home and the credit card statement arrived he had been charged $440. Budget are refusing to refund the money saying that he signed for it and my husband has now contacted the American equivalent of Watchdog.
Ridiculous surcharge for satnav with Dollar in San Francisco. And I am used to returning the car with a full tank, but somehow ended up with a "deal" that insisted on an empty tank, which was do-able for the first rental term, but not for the second, which was a short-term hire of 3 days pootling about and there was no way we could use a whole tank of fuel. They also charged us $70 for the full tank in the first place!
They also tried to "strongly recommend" we take out additional insurance against recovery of vehicle after a crash - but on reading the small print, I had to point out to the guy that we were already covered. He then double-took, read it again himself, and then muttered, "oh, OK then," and left it.