Would bad debt expense be included in the general and administration section or other income (expenses) on a multi step income statement?

I would prefer the latter.

I was told it usually falls in selling expenses?

In the U.S. bad debt expense does not belong in the "other" section. It's a selling & admin expense.

As for falling specifically under selling -- I doubt there's a rule on something like that. I look at it as the expense of not being able to collect on a debt, which I consider to be an administrative duty. I consider selling expenses to be those which are related to the process of selling itself. But that's my opinion.