I mean, purple literally blow themselves up for no better reason than to kill people for their ideology. You don't think similar extremists would just as readily take a presidential position with such stipulations.
A better way would just to have all assets seized after their term is up. Make it so they can't keep anything they might gain from it. Eliminates the problem I think.
When you become president, all of your assets are seized and assessed. They're then distributed according to, uh, groundhog farts or whatever, who cares.
After your presidency, you get a random assortment of new assets worth what you gave up on entry, plus inflation. Well, to the best of current knowledge and with little to no ability to predict future performance, though if they're sufficiently randomized and distributed, you probably won't lose everything due to a faulty swing in the economy. Hell, you might be better off if you weren't sufficiently diversified beforehand.
That way, getting into the presidency isn't a sacrifice, but it also isn't ripe for exploitation like having government meetings and foreign dignitaries at your own hotels, paying you. For example. Off the top of my head. Completely out of nowhere.
And any 'exploitation' you do to make sure you're better off afterward would necessarily be to better the whole economy, not just your little corner of it, because you have no idea what you're going to get. Similarly, the bribery and 'bribery' from industry would cancel itself out, because all assets are taken and randomized from the president so whatever million dollar babyfund you give their campaign or them will be obliterated.
The only problem is nepotistic exploitation, giving your brother-in-law's company a cozy make-work job or something. Dunno how you'd fix that unless you also randomize the assets of anyone related to the president.
/s