You lot been on the cider again?
Graham?
(I've fell out with my Missis and I've got the 'huffy bed' (sofa) - but never mind, it's close to the computer!).
Anyway, I think Graham is metaphorically intimating that 'Morrison's' shopping bags indicates that the householder is 'on a budget', therefore stuggles to pay their window cleaner a decent price.
However, I've recently had two 'run ins' with householders who drive large 4x4 vehicles (Shoguns I think they were), and both had fairly posh houses.
Avoid customers who drive black Shoguns! They're tighter than a mosquito's back passage!