Before we speak to the commission part, I would be more concerned about your bad credit if you are looking to rent. I personally have had my last three rental clients get turned down by several landlords , not so much because their credit SCORES were low, but because they have NUMEROUS late payments (the credit report shows how many were 30, 60 and 90+ days late). This type of credit history scares off landlords, regardless of your scores or your income. Landlords want to be somewhat assured that THEY will get paid as the eviction process is time consuming and costly.
If you are using a Realtor to help you find a home to rent, as the tenant, technically you don't always have to pay the commission. If the listing says the landlord pays commission, technically your first months rent will go towards the commission. So in essence you would be paying the first months rent plus the 1.5 months security deposit up front or a total of 2.5 months rent to start.
If the listing says tenant pays commission, then you would be paying 3.5 months rent ...1 month rent towards commission, first months rent, and 1.5 month security.
If you can explain the late payments (loss of income/job, banckruptcy, foreclosure etc), it would be wise to obtain your credit report yourself, and make a list of the why's to explain to the landlord.