Don't listen to all those who say that a car booter customer isn't worth having a go at, sounds like a bit of pessism to me, the only way to know for definate is to give it a go. Don't let that other guy who's already there put you off either.
I have worked the car boots for a couple of businesses over the last 15 years or so. I have taken tens of £1,000's of orders for a window/conservatory firm owned by a friend. I also used to have my own fire surround business and had a little display on car boots, took hundreds of orders. My father is a wedding photographer and started out on the car boots for the first couple of years to get his name kn own. The foot flow of people there is second to none. I'm not a carpet cleaner, just browsing in this section really, but thinking of doing a regular car boot for drive ways and gutter cleaning.
Go for it, you'll be surprised at the reaction. For the sake of £7/£8 and a Sunday morning, you'll be inundated with work. You'll also be surprised at the punter, they're not all lower demographic as some here would have you believe. You're always going to get the bargain hunter, but on the end of the scale there are loads of people who go to them and some are willing to pay your prices.
The only downside you have with a car boot is bad weather spoils them, but with this weather what do you have to lose?