I'm another regular renter - I've done it dozens of times and I've rented places in the USA, Spain, Portugal, Tenerife, Madeira and even here in the UK. So far no real problems. I might one day turn up somewhere and find I've been scammed and the place doesn't exist or else it's a slum. But then I'll just take myself to a hotel and count the fact I've been lucky for so many years as a bonus. So for what it's worth, my advice:

• Definitely avoid paying by Western Union - that's a well know scam. Use a credit card. If owner doesn't take a CC then go somewhere else.
• Do you homework and gauge prices in the area you are visiting. Anything that's way too cheap is a warning sign.
• If you're renting directly from an owner (like through VRBO) do talk to the owner and email them and ask questions. Get a feel for if they're genuine. Also Internet searches on their name / address / phone number can help you check if they're real people.
• If renting from an agency or management company then usual checks to see if they're legit.
• Make sure you know of any taxes and fees that you're liable for in addition to the advertised rental prices.

Sites I've used include VRBO /HomeAway / CyberRentals (all part of the same group). www.holidaycottages.co.uk www.ownersabroad.co.uk www.holidaylettings.co.uk Plus of course local estate agents, realtors and lettings agents.

Have fun.