Pretty sure this is false in most countries. You are required to disclose purchases and declare values, even for personal use. If they hit a certain thresholds, you’ll have to pay a tax.
Now I’m sure most people just ignore this, because practically they don’t know which items you carried with you and which you purchased. But it isn’t legal.
Yea, I go out of my way to Microcenter, passing several Best Buys.