You need to research the agents as a buyer. See how well they try to sell you a house you ask about, do they offer you the details of all similar proerties on their books, are they quick to get back to you, keen to set up viewings etc.
All indications that they will work hard to sell your house.
If the agent you think best based on this has a higer fee try to negotiate. I have always got them to price match their competition. You can also ask about a fee variation based on how fast they sell. So perhaps if they sell your house within 6 weeks then they get 0.5% more.
As for putting it on at a higher price than they have advised, well you can, they will put it on at what you want (within reason). But, I would advise you to get on zoopla and rightmove and look at the sold prices for similar houses on your street and in the area. That is the best indication of its value, and if you over price your house you will not get people through the door.
Equally, when you are looking at the house you want to buy, check the sold prices as best indicator of what you should be aiming to pay. If your house has dropped in value so have the others.
If you are in no rush you can try a higher price, but most likely it will just sit there and after a month or so you will be advised to drop the price to get people interested.