The European Consumer Centre is advising people to exercise caution when buying holiday accommodation online.
It says failure to prove that the purchasing website is genuine, can prove costly.
The 'book now, pay later' practice can, in some cases, be misleading.
Martina Nee of the European Consumer Centre says where possible, keep records of transactions.
"Well when you're booking holiday accommodation online it's extremely important to check how and when they payment will be made before the contract is concluded.
"Keep evidence of this, take screenshots," she said.