I buy a lot of the Wednesbury copper pipe from
Screwfix and Toolstation. Never had any problems with crinkling. Maybe it's down to the person operating the bender.
Put 25 metres of Wednesbury in my own house last week. Wouldn't do that if there were any doubts about the quality.I avoid merchants for the general plumbing stuff, and use
Screwfix and Toolstation. Prices are very good, and it all comes straight to my door next day.