I have booked flights and hotels all over Europe using Expedia.co.uk. In 2002 an online payment problem for a hotel in Italy was resolved when they called me and I was impressed.
Recently a hotel in Portugal I was booked into shut down. I received an email asking me to contact Expedia Lodging Operations to confirm a change of hotel choice they were proposing. They gave two numbers, one in the US and an international one. Neither would connect from Skype. I rang their UK number and was told there was a problem and that they would call me back to save me hanging on the phone. Ten minutes later I received a call to my Russian mobile from the UK, was thanked for my patience and then transfered to the Lodging guys in the US who then ran through some options and left me with an appropriate alternative. The email confirmation arrived before I had finished the call.
It seemed a bit long winded and at first I was a bit put out, as the reference number in the Lodging Ops email was different to the ref number in my booking from Expedia. Also, the contact numbers were not familiar. In the end though it was all genuine, the staff were, importantly, able to provide solutions at every step and were very polite.
Over more than ten years, these are the only problems I can think of. Some flight options in Eastern Europe are not covered I've noticed and the same goes for hotels which are not so western facing. I wish they'd connect up trains as well.
Overall, a good place to start at the very least and of the most trust worthy I've encountered.
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