score:3
It depends on the type of expenses.
On restaurants and hotels just ask for a receipt (and tell you need for tax reasons). Usually they provide you something real, and because both of you use the same reason "less taxes", they cannot really argue. Also tell in advance if you can pay with card (and maybe explaining that you want to keep some cash for minor transactions). In this case, if they refuse ("terminal is not working", just change restaurant: this is a major incentive: the lost income is very probably larger than the taxes they would "save").
For minor purchases, the two methods become inconvenient, so use your gut feeling (and maybe ask for receipt). but in such case, also the "stolen money" is minor. But I tend not to like such countries, and world is big enough to choose a new country to like (or dislike). OTOH lack of trust on government (and corruption) is not a problem tourist could solve (but we can help the honest people).
Upvote:-9
To minimize the global reward of VAT/tax elusion, I proceed this way.
I assume foul play in both cases (local business and credit card provider).