Thank you for all the replies so far...
Let me put the circumstances in a better light...the couple knows this is my first wedding and they're OK with it. They can't afford the average price (or even below average price) of wedding photographers here in South Africa. So the price I'm charging them is really a bargain. They still prefer somebody with professional equipment to take photos, than to leave it to family and friends with consumer cameras or cell phones.
There are a lot of people here who really don't want to (or can't) spend money on photographers, and I offer them a solution for a low price. If I can do a few weddings like this, my work & experience will improve, and then I will get more work in through references.
Some people have mentioned contracts. Believe it or not, here in South Africa, 99% of the time we don't have contracts when it comes to wedding photography. And if a couple is unhappy with the results after the job has been done, they rarely sue. It is just a matter of, the photographer will not be recommended and the couple will be very sour.
I decided to start wedding photography when I saw the results of two of my best friends' weddings (they got married a month apart), in both instances the photographer was considered professional with years of experience, and their portfolios looked promising. But the end results were bad, I couldn't believe it was done by "professional" people.
I knew I could do better. Although I'm new to weddings, I have previous experience in photography, I'm a keen aviation photographer and some of my work has appeared in international magazines. So I know something about photography. I know an airplane and a bride are two different things, but everybody has to start somewhere
I have done a lot of practising beforehand, even had two sessions with two couples (friends of mine) at typical wedding venues, practised both indoor and outdoor shots, experimented with different settings, fill flash, etc, and the results came out pretty good.
I've also visited the location last week, so I know what to expect in terms of opportunities. Will finalise my list of shots tomorrow evening. And of course make sure my Canons are loaded and ready to shoot!
Any more suggestions/advice still welcome!