Hi Gary, best thing to do is ask for the asking price before you view. The price will include the agents commission – unless you are going via a property finder who then charges you for finding the property for you.
Agency commission varies, standard rates are from 2.5% to 10% but again included in the price. Some of the higher fees are because the agent and property are logged onto a central sharing system in which case the fee is split between several parties.
Ultimately if you are happy with the property at the price you have it for then does it matter?
Good luck with your search.