depending on the marketplace.
If the marketplace is not that competitive create yourself a mini site register the URL in your name, optimise and get it to the top of a search engine (google is my choice), put a request more details form on the site and pass all the enquires on to your client as a goodwill gesture.
Once the site is getting quality traffic you then have a few options open to you and your client.
Bin it and optimise their site - whatever you tell them to do I bet they will bend of backwards to compile.
Sell or rent the site as part of an optimisation package to them.
See if there are any affiliate programs which you could use it for
Sell it to a competitor Ė never actually done that but it is always an option
If the marketplace is very competitive you need to think about the return. How much work is involved against what the client is willing to pay.
A good selling point is to point out to your client is the overture bid price if itís high you can prove itís competitive.
$5 per click average 1000 clicks per month = $5000 is what your competitor is paying for one SE listing and Iím willing to do this for you for $xxxx
If itís low get them to invest a few hundred $