How to bid on someone's service (NOT A WTB)?

How to bid on someone's service (NOT A WTB)?

I posted this question, but people did not understand what I was asking.

A buyer scrolled over to my service (not a WTB) a service of mine. As a rank 1, my price was at $30. He bid on the service (again not a WTB), a total of $3 for a service that I charge people to do $30. He was a level X member.

I want to know how I can do this, how can look at people's service they offer, and instead of paying the price they set, I want to know how I can bid on the service, thus getting their service cheaper than it is originally priced.

Please don't post here instructions for WTB because that is not what I am asking. Someone bid on a service and was able to ask for the service at a fraction of the price i could charge. I want to be able to do this, how?