Shoe leather creasing patters

I bought a pair of shoes (ankle boots actually) actually from Clarks
just before going on holiday for two weeks with them. Whilst I was
away the right shoes developed a marked amount of creasing across the
front of the shoe where it must bend whilst walking. The left shoe
has only slight creased. The creasing on the right shoe is far
greater than any other leather shoes I've had, and extended to several
other areas that aren't creased on the left shoe. As I was on holiday
I had to keep wearing the shoes. When I got back to home I tried to
get Clarks to replace the shoes, but the assistants insisted that the
leather didn't appear faulty nor the shoe, and they had to put it down
to the way my feet fitted in the shoe which wasn't their fault so they
couldn't replace the shoes (and I'd worn them outside too). As far as
I can tell my feet are the same size and shape, so I guess it must be
something wrong with the leather, but I'm no an expert and the
assistants wouldn't change their minds. All they suggested was that I
spend more money on things called shoes trees which pack out the shoes
when you're not wearing them. I left resolving to write to Clarks
directly to complain, but I was wondering if this has happened to
anyone else with leather shoes. Is it common for shoes to develop
completely different creasing patterns? The right shoe also feels
different now when walking as the increased creasing causes it to fold
deeper onto my foot, so I could use this as an excuse to go back to
them but it's not uncomfortable, just annoying.
Many thanks in advance for your help.