I've had to deal with difficult landlords a handful of times and I'd say the common thread is that they expect you, the tenant, to not understand your rights and the laws that enforce those rights. This is especially the case in low-quality housing units near universities, where students generally don't live in a single place for more than a year or two.
For example, one time a landlord didn't return the security deposit. I called him, messaged him, left notes in his mailbox. No reply. One month, two months went by. So, I looked up the relevant legal code, found the part that said "landlords have 30 days to return the security deposit with any deductions listed. Failure to do so results in the landlord owing the tenant double the original amount with no deductions." I printed that out, highlighted the relevant section, and mailed him a letter saying that he can return the original deposit amount to me immediately, or I will file at the local court and he'll owe me double. I got a check in the mail two days later.
For example, one time a landlord didn't return the security deposit. I called him, messaged him, left notes in his mailbox. No reply. One month, two months went by. So, I looked up the relevant legal code, found the part that said "landlords have 30 days to return the security deposit with any deductions listed. Failure to do so results in the landlord owing the tenant double the original amount with no deductions." I printed that out, highlighted the relevant section, and mailed him a letter saying that he can return the original deposit amount to me immediately, or I will file at the local court and he'll owe me double. I got a check in the mail two days later.