You might consider asking them to buy about 3 or 5 each of the lowest 3 denominations, whether that is 50¢, $1, and $5 or $1, $2.50 and $5. Or if the third is $25, tell them not to get that one if you aren't comfortable with it. I recently asked my niece to go buy a $100 chip, take good pics of both sides, turn it in for 4x $25 and repeat, then to get me the $1 through $5 from the Carnival Splendor.