Car washes and vending machines are bad places to hunt. Besides being caught looking crazy, and possibly verbally/physically assaulted, people that deal with coins tend to know about silver...
$5-10 dollars here and there.. not really that big of a deal, just don't drain empty.
That's actually how I first started hunting. My brother and I went to wash his car and he said that this quarter might be silver. I told him he was crazy and proceeded to using it. Later on I researched and found out that indeed it had been silver.
Sad sad day. Hopefully that '64 will finds its way to me again.