In brief, here's Susan's advice on what to ask potential Web designers (mushed in with a little advice of my own):
1) How many years of Web design experience do you have? (Five or more is best.)
2) Will you provide samples of websites you've recently designed? (Visit them, while imagining yourself in the shoes of a donor, potential funder, or member of the public looking for information. Then see how well you can navigate around and find what you want.)
3) How do you price your services? (This may be by the hour, or by project. If it's by the hour, also ask whether different tasks are billed at different rates.)
4) May I contact three of your references? (Don't skip this step! There's nothing like hearing from others that the designer was easy to work with and followed through by creating a site the nonprofit is still happy with -- or not.)
5) Can you draft a design agreement with an estimated scope of cost and turnaround time? (Don't get me started on the weaknesses of verbal agreements, or of not discussing what's expected in advance, in detail.)
6) Will you be available for follow-up questions or to discuss a page design? According to Lee, she's heard many stories from clients who'd hired designers who turned out to be unreachable!
By the way, these are important questions to ask even if a volunteer has kindly offered to design your website.
Volunteer help can be a great way to save money in the short term, but unless the person is truly qualified, lead to long-term roadblocks in the workings of your website.