I think that is a good recommendation. I have seen, once or twice, an entry where the owner obviously mistyped or made a mistake in the data causing a strange outlier data point. (Such as the SUV which had been averaging 13ish mpg suddenly getting 54 mpg on one tankful.)
Yeah, that happens all the time and people often go back and fix them later. But by then, the numbers have gone out for everyone to see.
I think that's just one of the hazards of the site that we'll have to live with. We could hide/color best tanks that are over a certain amount, but people will learn to ignore those, and then the point where we draw the line will always be in contention. We have data limits in place in some places already. For example, you can't add more than 100 gallons/fuel-up (or something like that) for a car. We continually get emails from people asking to raise that limit. I think any number we choose will upset someone.
So I think it's better to live with some inaccuracy on this than try to solve it with a technical solution.
I think maybe a warning would be appropriate when you try to enter a tank that's, say, 80% higher MPG than your current best tank.
Browsing through cars with 100+ fuel-ups, I've found a surprising number of them who have a best tank that's twice their average, clearly telling you that they missed the fuel-up but added their mileage to the next tank. You'd think it would be obvious that your SUV or V8 sedan can't do 50mpg. When you're looking for a representative figure on fuel mileage, you look for cars with lots of fuel-ups, and then when you see an unbelievable best tank number, it throws doubt on the accuracy of the mileage history, since you don't want to look through 100+ tanks to see how many times they put in bogus fuel-ups.
Well, we err on the side of just adding the data. It sucks when you're at a pump trying to add a fuel-up, and you get tons of error messages that the data isn't quite right. I'd rather have people enter bad data and fix it later, than be sitting out in the world yelling at the screen to just add the damn fuel-up.
I totally hear you on the bad data showing up publicly, and maybe we can tweak the best tank stuff a bit. But when you're looking around comparing mileage stats, you're more often looking at average MPG than these outlier best tanks.