You are right, there are a lot of designers out there. To put this in to context there are also a lot of car mechanics and some are better or more reliable than others and I believe the web is just the same.

You did the right thing, obviously having prior knowledge helped in finding the right man for the job. Personal preference is also a key decision maker as some designers have stronger skills in certain areas whether it be app design, ecommerce, grunge etc.

The few things that I can advise are;

Research into the kind of design you want.
Find samples of their work around the internet.
Ask if you can speak to some of their clients.
Plan out your project in full and agree times/dates with the designer/developer.

At the end of the day prior planning prevents a lot of unnecessary issues cropping up during your project.

Gavin

I ended up choosing a well respected designer because of his reputation; I knew I’d get something I was happy with, and I wasn’t wrong. I’m fortunate enough to generally know who’s who with web design because I’m an avid user of Twitter, and it generally seems to be web professionals who mainly use Twitter (or at least it was before it went super mainstream). Names get bandied around via ReTweets or links to blog posts of developers etc. Unfortunately it’s not the case with a lot of other people, and some prospective clients will turn to trusty Google to find a ‘web developer Glasgow’. These results almost always return badly designed sites put together by people who have the most basic of web development knowledge. Bottom line is, I think it’s hard for people outside of the loop to know where to look, and that’s even before the budget or what sort of developer you’re looking for comes into equation.