What's the big deal with shops? If Mrs Brown and Mrs Smith get cleaned every month or 8 weeks etc, they could only take about 30 minutes to clean and pay 40 quid between them. Most shop fronts may take 10 minutes and only pay 4 quid. If you haven't got lots of compact shop work, why chase after them?
In my time in this game, I've found the majority of shops aren't too bothered about standards, and not only that, most will drop you for a new guy for less than a quid. We do a few shops locally, because they are on route to other work. A petrol station is on route too, and we charge less than 7 quid on that. Takes about 10 minutes, but as I said, it's on route to domestic work.
If you look at the time taken and the end earnings after costs, you need to think if it's worth chasing crap work like shops.
Gav is a good lad, and has put a lot of faith into that sort of work. Good for him, Dave Morris makes it pay too, but it's not all milk and honey IMO. I'll stick to mostly domestics. I leave the shop stuff to those who know how to make it worth doing.