“The way I look at it is that people know that the Mechira is not that good and it would definitely not hurt to be machmir”
chas veshalom to say such a thing about frum yidden.
All frum yidden view the sale as perfectly good. The Chasam Sofer writes (OC 113) anyone who questions the sale should be yelled at.
Chas veshalom to say it was “questionably sold” You are besmirching Gedolei Achronim and the greatest poskim today ALL of whom orchestrate mechiras chometz,
sure there is a hanhaga not to sell chamutz gamur. But that is not the discussion at hand we are not discussing you selling your chometz.
You cannot find any teshuva backing up your mistaken shitah. True Maaseh RAv does say that the Gra did not buy chometz sold over PEsach this was addressed in my 2nd comment in this thread