The landlord is trusting their tenant with a huge asset, the home. It's easier and more common for a bad credit risk person to influence a good one toward bad than the other way around. Looking at the past is not a perfect guarantee of the future, but it's what is available. The home owner/landlord needs to determine who they are trusting with their asset.
There are good people with tough histories. I've worked with many and overcome my own issues, but trying to hide them isn't fair. Prepare a letter of explanation of your partners issues, what happened, why and most importantly why they are not going to be repeated and you may get a landlord to listen.