I've watched many magicians work at wedding fayres and many of them make a very costly mistake.
Over the years I've attended hundreds of wedding fayres and have found them to be a great way to fill the spaces in my magic diary. Today, I only attend them if they have the right demographic for my fee's, or if I'm fronting for an agency and can pass the work on. However, they are an easy way to reach hundreds of cleints that are about to host the biggest parties of their lives. If you want to start off as a paid magician, they are a great way to build up steady work.
YOU SHOULD NEVER STAND BEHIND YOUR TABLE
It always amazes me to see magicians standing behind a 6' table waiting for people to approach them and ask about the magic. That's just madness! The secret of getting a lot of gigs from a wedding fayre is to get out into the flow of people and talk to as many as possible. Like any form of direct marketing, it's a numbers game. The more people you 'touch' with your magic, the higher the conversion rate. By all means, set up a great display, but then don't become trapped by it. I just have a simple pop up banner and a small close up table. It allows ME to be the feature of the stand and build a crowd. That's what brings you work.
View EVERY couple as a potential gig, and keep on your feet the whole time. Use just one or two tricks that you know will get great reactions, and repeat them to everyone that you can. Move around the room. Perform in the cafe area in the reception, even at the top of the stairs. Although you should not stand in front of another exhibition stand, you are free to move around and you should use that to your advantage.
In summery, if you want to get the most from a wedding fayre, you need to make sure EVERYONE gets to see your magic. It's so easy to prejudge people if you don't make the commitment to perform to everyone. Prejudging people is terrible marketing, so avoid it at all costs. If you stand in front of your stand and perform continually, you will find that wedding fayres can give you many many times the return on investment that any other form of advertising for your magic ever could.