Do I have to pay the rent in advance?

In most guest houses the answer is yes.

For short term stays one or two days, sometimes a week or two, you may be able to pay at the end of your stay. If you need to pay a deposit this will need to be paid in advance.

For longer stays 2 weeks or more most ask you to pay in advance.  You will most likely be asked to pay your rent one month in advance. Usually by the 25th of the previous month. So Junes rent will need to be paid in full by May 25th.