Wow! These are out and out crooks!
I booked the car through Booking.com for 8 days car hire from Lisbon Airport, and also took up their insurance policy. Good price, so far so good.
When I picked up the car, I felt there was something off, they tried to sell me their own insurance (not sure of legality of multiple insurances) but politely declined. I allowed their hefty deposit to be held on my credit card, but my suspensions made me take photos and generally be super vigilant of the car. When I returned the car, with full tank, and in identical condition as picked up, the inspection seemed to go well and car was accepted in good condition. I was asked to sign a digital form that also showed there were no problems. I was told the receipt would be emailed.
No email arrived and £182 taken from deposit with no explanation.
Booking.com are looking into this, but have not communicated with me at all.
So, I decided to use live chat with Goldcar (4 hours later) and was told there was a problem with the wheels. I have photographs to prove car was in good condition and have insurance to cover any damage. But Goldcar are unscrupulous and dishonest.
Please make sure if you're using them to have as much evidence as possible, photographs of car, petrol receipt and take a picture of tablet with your return form, as you won't get a copy on email and it can be altered to support their story after you sign it.
The money stolen from me is more than the cost of hire and insurance for 8 days.
I'd strongly recommend not to use Goldcar, but make sure you're covered if you do.