I switched the brokerage for a taxable investment account last year. The new brokerage reimbursed the transfer out fee of $50 from my old brokerage. I don't have my 1099s yet but I noticed in the online tax information at my new brokerage, it has that $50 as taxable income. Is this correct? Since it's a reimbursement it doesn't seem like it should be. Unless perhaps my old brokerage would put -$50 on my 1099 from them? That seems unlikely though.
Since it's not a rebate (i.e.: reimbursement of money you paid to them), it is a taxable income. It is essentially a sign-up bonus, they have no obligation to reimburse you for anything by law.
This is usually reported as interest income or MISC income on 1099 (if it's MISC - be careful to mark it properly if you prepare your own taxes, otherwise it may be added to your self-employment income).
The $50 you paid as the transfer fee can be deducted as investment expense, subject to the 2% AGI threshold.