You have managed to find one client and your worry is finding clients you can trust?
Get clients first, then start worrying about getting screwed over when you actually start getting screwed over. At this stage, getting screwed over isn't so much a problem when you are new and looking long term.
However, it's never fun to work for free. On Elance and Odesk you can do the hourly option where your invoice is auto pulled from the buyers CC every week. You could do a 30 / 30 / 40 scheme where you get 30% down payment before you get started. You could get a down payment and then send an invoice weekly. With these schemes, even if you get screwed, it won't be for much.
Personally, in six years of doing freelance web development I have never been screwed over. A larger worry is generally the payment / headache ratio. Some clients are so great to work with that you feel like it's the easiest money you could possibly come across. Other clients are such a pain that you feel like you have to claw and grind for every billable. In some cases, it's better to get screwed over by a bad client and halt the project rather than grind it out for weeks / months and be burnt out by the time it's over.
While you will likely not have to deal with getting screwed over often, slow payments will be a much bigger problem and can hurt you as much as non payment. The same payment schemes apply. If a payment doesn't come through, then pause the project.
As for server access, this is very typical. Most clients will hand you their server access. Again, I have never had problems with this. An overall better method for handling development is for the client to give you access to a repo which is hooked into some sort of deployment scheme. In this case you wouldn't touch the client's server. However, not everyone will know how to set this up, so perhaps you could offer this setup to the client as part of your gig.