Orlandovillas.com is run by two guys based in England. They invite private owners to advertise on their web site and also they advertise their own private homes on the site. It is a very successful site and as long as you do your homework you shouldn't have any problems.
If booking with an owner, make sure they have a local management company, that the terms and conditions are acceptable to you, that the home is indeed equipped with everything advertised, that it actually exists and is in the location that you want. It doesn't harm to find out who the MC is and to do some checks on them, such as members of Better Business Bureau, Chamber of Commerce and CFPMA.
One trap you mustn't fall into is the price one. Not all homes are the same. Two identical homes side by side can be very different in terms of layout and how they are furnished. Price is not everything..just make sure you get what you want at the price that is affordable.
Finally, on price....make sure whether the price is US dollars or UK pounds sterling. I suspect this is a price in pounds sterling unless you are going at a very quiet time of year.