I personally have never had a situation where I put another casinos tokens in a machine. When I encounter a foriegn token from a machine I usually just keep it for my collection. I have noticed on a few occasions where I have gotten tokens from a casino other than where I was playing. In fact, this is a good way to get tokens when starting out. Whenever I win something on a $1 machine I always look through the tokens before playing them back. I have received numerous tokens this way. There are a couple places in LV where I have gotten several. Other places though, as Gene says, may have their machines set to reject them as I do not always find foriengn coins everywhere.