"For 20,000 miles I get an upgrade"

Ever have this happen. I call the airline and say I would like to use 20,000 miles and up grade. They say no seats are available for mileage upgrades on this flight. Then you get to the airport and they upgrade you for free.

I've had it go the other way also. Give them 20,000 and then get upgraded and see empty seats you could have had for free. Barry