I have been with MindMyHouse since 2009 and obtained 11 sittings with them in 2010… Over the years they have added many features bringing it up to date with other sites. It is free for HOs and about £20pa for sitters. After about 5 years I was given a free year as a thankyou.
I joined AussieHousesitters for a year and was successful with my first application. One of the best features of this site is that you have points deducted for not responding to a sitter or HO within 5 days, then more points for 10 days and so on.
It is interesting to note that you can join a few sites and the total cost of them all will be less than the annual THS fee.
As far as I am aware no other site asks for ID or security checks.
On the new ID and Background Check thread, someone recommended that those of us who will be leaving should copy all of their reviews before they are barred from using the site.