I've always been slightly put off buying meat/fish from most of the butchers/fishmongers along Peckham High St after seeing them manhandling the meat along the street in old shopping trolleys first thing in the morning while wearing 'whites' that look like they've never been washed. In comparison to other butchers that I've seen, the hygiene standards put me off a little. The smell can also be overly pungent at times that puts me off.
The Chinese supermarket across from Primark has gorgeous fresh fish. Their king prawns are amazing.