At least for Euro coins (are these more difficult to fake?) it often happened to me that some vending machine accepted a coin only after multiple tries.

What might be fun to try is to use a Euro 5c coin in a machine that expects 20p sterling coins. Living on the border with Northern Ireland, we figured out when I was young that the sweet machines in Northern shopping centres could be conned like that.

The old (pre ~2005) New Zealand 50cent coin was a match for 5 franc coin in Switzerland (~5USD). I knew postgrads that would always stock up to use in vending machines, after finding that out I've always been curious to know how much research a mint does to prevent this from being possible.

>I've always been curious to know how much research a mint does to prevent this from being possible.

At the Canadian/US mint, seemingly zero.

US 5 cent coins (aka nickels) are (or used to be) the same diameter and weight as 20p sterling coins as well, as a grad student in London I may have accidentally used a few in vending machines and doing laundry...

In the 80s I was able to use 5p coins (same size as the modern 10p) instead of quarters in arcade machines when I was on holiday in Florida.

The same trick worked with Australian $1 coins going into machines expecting NZ $2. imho having $1 larger than $2 isn't right.

Same for Euro notes. It often takes multiple tries of trying to straighten out the bill before a vending machine will eat it.

Yes, but I've been conditioned into thinking a fault with the vending machine is much more likely than a counterfeit coin. Just the other day, I was using a vending machine that had a special panel on the front of it, with the specific purpose of rubbing your coins on it in the event that the machine didn't recognise them!

I've definitely noticed worn coins before. Some of the current pound coins have been in circulation for 34 years, though, so I'm not surprised there'd be quite a range of wear.