> Buy a cheap smart TV and run it in "store mode".

They aren't "cheap," but just last week I unboxed and tested 5 different Samsung S95F televisions of 4 different sizes.

One of the functions that each of them promised to perform when set to "retail mode" was to reset the picture settings every 5 minutes.

That makes retail mode a non-starter for anyone who seeks any resemblance of accuracy in their video system, at least on these particular televisions.