An agent we used to work for,demanded that we "load" our invoice by 10%.
Ie if an invoice amount totalled £100,they wanted us to invoice them for £110-00.
They would then present this invoice to the outgoing tenant,and get the full inv amount from them,and then pay us £100,so all our settled invoices would be 10% short.
I told them if they wanted to extort money from their tenants,they should do it under their own letterhead and not mine,and had nothing to do with it as I considered it unethical business practice.
On the subject of paying for work,there is no guarantee that you will get any work,but 20 squid is not much to risk anyway.
We have also had numerous scams offered to us asking to pay for work,costing anything up to £800 a year.
Personally,I would never entertain it, it is down to the individual if they take up these offers or not.