I think an even nicer solution would be a custom tier generator that allows you to drag a slider with the planned quantity
Then just a fixed over usage surcharge
Finding customers is always a tough task. We started from μ-ISVs with simple Windows applications to probe the market and see whether people are ready to buy tests and QA as a service and then slowly expanded the offered services list.
We have great customer retention (excluding some specific one-time projects, like a penetration test), I hope due to our dedication :)
I would say manual tests are most popular, and then load tests, then automation. Often customers start from a tiny manual test and then use our services more and more, in other QA areas, being happy to receive all of those from one window in a unified manner.
I actually run a small QA-as-a-service company (for 3+ years) and I should say that we strive to distance ourselves from "freelance" word as much as possible.
As most other cheap labors in a remote freelance mode — it is discredited. I think it would be just hard to build a personal brand strong enough to compete with tons of people, who can look like a diamond on a pre-sale phase and then just disappear.
I've got a few filing folders with binders, each with different color of cover: red for bills, green for hardware guarantee docs, yellow for various (mostly government) docs.