People often do research when buying a car to find one with few problems and long history's of reliability. You also chose a need specific one in the colour of your choice.
People buy and rent property based on location and affordability. Hence they end up with dogs often
The point your missing is mould is not the result of a break down or failure in the fabric of the building. Theres nothing to "fix" unless an extractor fan is broken or air bricks have been blocked up
Its a problem inherent in all properties designed and built up until the mid 00's what your asking for is an upgrade.
Its a lot worse in properties which were designed with ventilation from open fire places which are blocked up and or removed and where sash, crittle or casement windows are replaced with hermaticly sealed double glazing.
Cavity walls were designed to prevent penetrating damp
Later they were insulated to help with condensation
Later still the 50mm cavity was increased to 75mm and insulation installed
Later still that insulation was side fixed and the cavity upped to 100mm
All to combat heat loss and condensation.
Buying or renting an old house and moaning it has condensation issues is like buying an old car and moaning it doesent have Bluetooth connection for your phone.
In most properties the problem can be managed with heating and ventilation but the heating must be background temp of 20c at all times with boost during periods of occupancy and the ventilation must be fixed (no trickle vents that are closed by the tenant)
Opening windows is not efficient, and not secure (even on a half latch)
Insulated air bricks are preferable to standard air bricks (Note pic above with heavy mould around the vent)
When mould becomes noticeable it MUST be managed with antimould products before the expediential growth results in a bigger problem
Air space must be left behind objects on all external walls.
Most responsible tenants and home owners do this once they understand the issues ut even then SOME properties (basement flats etc) are just impossible to fix.
Then you need to spend significant money to sort it out.
Walls need to be lined with Thermal board, positive pressure fans installed passi vents fitted and antimould paint throughout. 20K should cover it
Thermal board on one of my flats
20181217_090359 by markchase8, on Flickr
SO you hit the landlord with a 20K bill and guess what? the retired couple who baught the flat to let out as a top up to their pension, don't have 20K
Remember 85% of privately let properties are owned by single property non professional land lords
Caviet Emptor. Be careful what you buy or rent
Ensure the property has agreed repair periods of essential and non essential repairs, ensure older properties have had measures installed to prevent condensation. Ask to speak to the previous tenant, check for mould in key areas like toilets kitchens and bathrooms and around the windows. Be cautious of recently redecorated walls in those areas. Pay for a pre rental inspection by a qualified surveyor like me and expect issues in older properties.