Estate Agent Fees?

[yelenots]

My mother owns a retirement property of which I am trying to sell for her in order to pay for her nursing home fees.
I am in the process of changing estate agents as the one I'm with at the moment is rubbish!
Can anyone explain why some agents have offers on to sell property for a set fee i.e. £600 but when i tell them its a retirement flat it suddenly goes up to £1700+ when exactly the same work is involved? Doesn't seem right to me!
Thanks

[bednobs]

perhaps you should ask them. My guess is that they advertise the set fee offer, and no-one gets it - they always find a reason to increase it

[ummmm]

They usually charge a percentage.

[rockyracoon]

I reckon it's because they know you have to sell, either for nursing home fees or though inheritance, most properties of this type don't allow subletting so basically agents have you by the short and curlies.