Batman Sells Out!!

You know, if he weren't already a kajillionaire, this would be a pretty clever way to "sell out":

Of course, these days a million dollars is a rounding error to Bruce Wayne. And given that the ever-increasing circle of those who already know Batman's secret identity probably numbers in the hundreds, you could almost certainly buy the information for considerably cheaper from, say, a disaffected Hush henchman.

But why would Batman "sell out" in the first place?

See, exposure to "epsilon rays" caused Joker and Batman's minds to switch bodies, because science.

So, wait. Why didn't Joker just take off the mask and look in the mirror, for his own satisfaction, before promising to sell the information? Why wait, and then have the epsilon rays wear off, and get nothing from the whole magillah?

Because comics.

From Batman #85 (1954), as reprinted in Batman #182 (1966)