I've had it happen as well & got stuck with a 100 peso fake - I wasn't a happy girl. I've also had ATMs give me torn (aka unusuable) money. In that case, the bank (HSBC) was very good about exchanging the bill for a real one when I went to the teller.
Count your lucky stars then Lee! I have had it happen to me probably a half dozen times and I only take money out of ATMs. Now some of those times were when I got change I'm sure but most of them were bad money from banks.
I've gotten extra vigilant about checking money now - seems to be 100 pesos notes that are the worst but have gotten a bad 50 peso note as well.
Are the fake bills easy to tell apart from the genuine ones?
100 peso notes seems to be the most faked one. By getting lower denominations, we should be safer and less likely to have problems. Besides I hear 100 peso notes are sometimes difficult to change. What are the chances of a bank teller passing you a fake note? Thanks.