Do I have to pay a retainer over the summer?

It is common practice that you will be expected to pay rent over the summer, even if you choose not to stay there during that period. Find out which landlords or estate agents are affiliated with your institution. If your university is prepared to recommend them, then they should be trustworthy.

Note that letting agents may charge you for reference checks, for drawing up contracts and for placing you with your student accommodation (usually up to two weeks rent), but they cannot charge you for simply showing you around the place!