If it is a private let - get everything that is said written down!!!
I rented privately and at the meeting I asked the L if it was ok to get pets i.e. cats. Her response was "you can do whatever you want to the house". Now being a responsible person I took that with a pinch of salt and put up pictures/mirrors etc. When something went wrong and the shower was out of use for 2 weeks, I asked for a reduction in rent. Got an abrupt and rude response about me keeping pets.... Property was sold shortly thereafter!
From a letting agency - FEES FEES FEES!! Why charge for example £210 for printing of a contract, doing a credit check, letting me into the property, doing a final walk through - this is total took about 10 minutes - rip off!
Quarterly checks are too much - six monthly would be appropriate unless there is something untoward going on in the house. Oh and if your tenant tells you that it is not suitable for you to visit the property, don't let yourself in (happened to me!). Not on!