If you've got the average rates I see on AW, I'd say that you're doing pretty well. Depending on how many hours you're available, if you're charging £120-£150 an hour, you're doing three or four bookings. It can be hard to schedule more than that in 6-8 hours. Because they're always wanting awkward times.

If you're turning down bookings because you don't have more room in your schedule, you can raise your rates.