It's a weary traveller's worst nightmare to turn up to a hotel and find it has no record of their stay. But that is an all too real scenario for some hotel booking site users, according to research from Which? Travel.
Sites like Booking.com and Expedia allow users to scroll through hundreds of hotel listings, comparing room prices and guest ratings side-by-side.
But arranging overnight stays through a third party can create its own set of problems.
When we surveyed 4,600 Which? members about their experiences of using hotel booking sites, 7% told us they'd had problems. Here we reveal the five most common issues they faced.
Our recent investigation showed just how different the reality of a hotel room can be from the glossy promotional images.
It was similar story for our survey respondents: 14% of those who experienced problems told us their accommodation failed to match up to its description online.
One guest complained of a property which smelled of mould and mildew, with a blocked kitchen sink.
Another reserved two twin rooms through Booking.com, only to end up with a small double and a sofa bed of 'truly appalling quality'.
'The hotel told us they give their best facilities to guests who book directly with them,' they added.
Never mind an inferior room, 13% of guests who reported problems turned up to no room at all.
On arrival they discovered that the hotel had no record of the reservation they had made through a third-party site.
In many cases, the manager was able to honour the booking. However, some were less lucky and found there wasn't a vacant room available.
One told us: 'We booked in good faith but, on claiming our room, the hotel knew nothing about us. To their credit they eventually managed to find us another hotel, but it was further away from where we wanted to be. I will be very wary of using Booking.com again.'
Booking.com told us that giving customers a smooth experience was its 'top priority'. A spokesperson added: 'We are available to answer any questions or concerns they may have 24/7, especially when in the very rare instance, something unexpected may occur at a property.'
The third most common issue was with payment.
A common complaint was confusion over whether the room rate had been settled by credit card in advance or was expected on arrival.
This led to some guests being charged twice for the same room.
One told us: 'When we arrived, the hotel had no record of any payment although I had paid Travel Republic a few months previously. I had to pay up there and then, but did eventually receive a refund.'
Following enforcement action from the CMA (Competition and Markets Authority), booking sites have committed to be more transparent about extra charges.
From 1 September, the headline price must include all resort fees and city taxes - so there are no nasty surprises at the checkout.
However, 5% of those who experienced problems told us they had been charged a booking fee.
As one confused user explained: 'I paid a booking fee to Owners Direct, but I thought I was paying a booking deposit. Then the owner asked for a booking deposit and it all got out of hand.'
The same guest was even more disgruntled to discover they could have saved nearly 15% by booking direct.
We received several complaints that booking sites aren't always clear on their cancellation policy.
One guest believed they could cancel 48 hours in advance without penalty, only to find contradicting terms and conditions in the small print.
Another user, who had to cancel a trip due to injury, told us: 'I expected to be liable only for 50%, but was still charged the full cost by the guest house. Booking.com had not told them of my cancellation.'
Less common problems included finding the same hotel cheaper on another site, double bookings and special requests not being passed on to the property.
Two per cent of those who experienced problems even reported turning up to find their accommodation didn't exist.