Be careful on this one, bluesky1
In effect I think the agent, is trying to get you on the cheap, no two properties are alike, even if they are the same size/area. imagine you have quoted a flat pricefor let's say a three bed semi, £250, property 1, fair condition, semi - maintained, no rubbish, result a profit. property 2, Poor condition, not maintained, middle amount of rubbish, £250?

The agent knows when he needs property cleaned, let him supply you with a weekly list, go round each property and fax him the price of each individual property.
Regards,
Bob