My experience has been that I my eyes aren't very good--pitchers I think are throwing hard are actually at 79 mph, guys who look like they are just tossing the ball may be touching 90. For me, it was worth a couple of hundred bucks on eBay to get some objective data. When an event puts velo info on the scoreboard or online, I just take their word for it.
I don't think I'm "that dad." But then, those guys never think they are, do they?