Our property was trashed, graffiti on the walls, weird cat claw marks up the walls when there was no pets. Dirt, rubbish, horrid, that year it wiped out any profit whatsoever (as whatever some people on this thread may think, landlords have to pay tax of 20-40% if personal income, then landlord insurance, gas safety certificates, tenancy finding services, and any maintenance, plus if you have a BTL mortgage, then a few hundred on that, so it can be hard to make much on that in a bad year).
Watch Nightmare Tenants, Slum Landlords.
Some of the landlords on that are appalling, and they tend to rent to vulnerable people such as recent immigrants or very low waged workers who won't have much choice.
Some of the tenants are appalling, and genuinely can cost £10,000 to repair a house that has been trashed, even just to remove the rubbish, replace furniture/kitchen cupboards and so on.
You cannot just believe the best of people, you have to hope for the best, prepare for the worst.
Unfortunately due to the lack of guarantees and the risk of one bad tenant, this has created an unsustainable rental market for private landlords as they have no incentive to take risks on riskier or more vulnerable groups- such as single parents, low waged or unemployed, people on benefits, people without large deposits. The councils are trying to remedy that say by lending deposits but it doesn't sort out the root of the problem.