Don't assume that we all have tech co-founders, as that is not the case or we would not be here.
I believe that you must vet both the person and the idea. That is done through taking a long look at their last few ventures/projects and understanding what went wrong (or right) and why. Ask for references and do your homework.
Ideally FD will provide you with enough references just through the platform that you can get a preliminary comfort level. Then you MUST meet face to face, even if not in the same city. If you are going to be connected at the hip, then you have to be willing to make that investment of time and money to travel.
On the idea side, if it is out of your domain expertise, you will have to rely on the work that they have done in putting the business plan down on paper. Look at competitors in the space. See what you would be up against and whether the idea is truly game changing or just incrementally better than what is out there. See how big the competitive field is and who the major players are.
You also must decide what stage is ideal for you to get involved in the project:
1. IDEA stage - you have more chance of influencing the technical direction and the product roadmap, but will have to wait longer to see a return from your investment of time. Your equity would be greater if you come in at this stage.
2. MVP already done - Even if the MVP is already in place (as mine is), there is still an opportunity to influence the long term architecture and the product roadmap. Often, the base MVP will have to be rewritten, but due to market success with the product (or some level of failure), you will be able to do so quickly and with much more intelligence and insight than the original speculative MVP. There will be less equity at this juncture, depending on how close to break even the venture is, but it can still be worth your while. If there is already revenue, while it may not be enough to pay a salary, you may be able to do a revenue share deal in addition to milestone equity to accomplish the specific elements of the plan to move things forward.
That is my preferred method and I am currently seeking a tech co-founder. I'm in the second scenario.
As to the "top level of accomplishment to expect", I'm not sure what you are referring to. If you are talking about the track record of the entrepreneur, don't be put off by failure. Failure is the best teacher. Those that have successfully built and flipped their companies likely already have the tech co-founder network to draw from. If you are referring to their experience in their field, I happen to think that this is essential. If they have been an executive in their field on the corporate side, that can mean that they have a strong network to sell to with their idea/product.