If your local hairdresser gives you a cheaper price when paying cash, wouldn't you assume tax evasion? (criminal).

Someone selling a used bike, or other items of similar value, on second hand market and not accepting Swish would maybe not directly be considered criminal, but would for sure raise an extra eyebrow about the origins of the goods.

Otherwise correct, nobody would blink if you use cash for other daily purchases like ice cream or groceries, even if unusual.