I've done some work on pay per lead basis. One thing that helps conversions is having a slightly different reason for them to convert than everyone else.
e.g. in my niche, everyone has the standard form to conversion. I added in a 'buy two, save even more! Request a quote here'. Nobody in my niche has this. Heck, I didn't even have it until last year. One of the best conversion things I've ever done.
Here's a question for the knowledgeable though. If you are selling leads, what's better, a paid listing/directory type service? Or a per lead.
I'm wondering because an old business parter just approached me with an idea for a service that could hook us into 10's of thousands of potential clients. Basically we're selling employee related stuff to employers. If I've got the employee at my website anyway, I could offer them additional services (i.e. generate leads). Would I be better to pay for a directory (user clicks and selects a 'nearby' vendor). Or would I be wiser to just have them fill out a form and then sell that name on a one-up basis?
Yes, USP's (Unique Selling Points) make a huge difference, anything you can do to make yourself different can reap massive rewards.
Per lead has always worked best for me as you have much more control and the payouts are much higher. It's all about testing though, you could start with Per Lead and then do a test with directories at a later date.
Mail me if you want some individual help on how to make more money.