Why is a security/key deposit required ?
The security/key deposit is actually a slight variation of the procedure that hotels operate by swiping a guests credit card when they check in. However hotels have no limit on what they charge to the credit card if a guest causes unnecessary damage.
Unfortunately in the early years of operation we had a small number of people who did not show much respect to the properties they had booked, caused unnecessary damage or just left the properties in an unacceptable condition i.e. left food items lying about, dirty dishes etc.
It not expected that guests should clean properties but it not unreasonable to ask that items like crockery are put back where they were found and all garbage is bagged up and ready for cleaners to take away. The small security/deposit of either 100 pounds or 150 US/Euros has pretty much stopped these issues by giving most guests a subtle mental nudge to perhaps put things away and tidy up. In the very exceptional cases of blatant disrespect to the properties and damage has occurred, 100 pounds rarely covers it.