The answer will depend on which country's currency the question is about.
Mostly Euro coins as the Euro is the local currency, however any coin from any country can be thrown in.
They do, although I don't know how widely they circulate in the country.
It depends on which country's currency the question is about.
Belgium. But any coin with the name "Belgie" (French for "Belgium") is now obsolete. Belgium switched to the euro in 2002, and euro coins don't carry country names.
They are probably using their promo coins to purchase your products. You don't get any money if they use promo coins.
What country? What denomination? If American coins, are there mint marks on any of them (small letters D or S)? Please post a new question.
The answer depends on the country whose coinage you refer to. Different countries have coins of different values.
Please be more specific. What country are you asking about? The U.S. didn't mint any dollar coins dated 1975, nor were any U.S. coins minted in the 1970s made of gold.
British 20 Pence coins have no country name on them. 20 Pence coins from any of the British Crown Dependancies such as Jersey or Guernsey, or from an Overseas Territory such the Falkland Islands will have the "country" name on them.
Please be more specific. What country are you asking about? The U.S. didn't mint any dollar coins dated 1975, nor were any U.S. coins minted in the 1970s made of gold.
No country could afford to make general circulation coins from precious metals. The value of the gold would greatly exceed the face value of the coin.