Perhaps you should go in with 'a couple of hours, a bottle of Flash and a hoover' and see how far you get? 
New tenants expect/demand a good level of cleanliness.
As a landlord myself I know it isn't just surface dust. It's things like:
irreparable damage to carpets
marks, burns and stains on floors and worktops
chipped tiles
doors, locks and window latches that have been forced and broken
curtain poles pulled out of the wall
grease all over the kitchen where cooker hoods filters are never cleaned
smashed plug sockets
boilers, meters and radiators that have been tampered with
mould and mildew around windows where no-one has opened a curtain or aired the place in over a year
rust on the radiators where people have draped wet washing for months on end, (this corrodes the radiators and they have to be replaced which is very expensive with labour costs)
built up grime and limescale and revolting scum in the bathroom that would take a deep industrial clean to put right
appliances that are so dirty/misused they cease to work properly
thick yellow nicotine staining over everything
doors pulled off hinges
mucky handprints up walls etc., that mean only a full redecoration will suffice
children's scribblings on the walls
a totally overgrown garden strewn with rubbish.
furnishings removed/dismantled/broken or otherwise unaccounted for
These are the very common realities faced by landlords every day, or at least the ones who are brave enough to let to certain categories of tenant (not always, but often.)
All that does not come cheap and it takes a bit more than 'a couple of hours with a hoover' to put right. Reality is, you could probably spend a minimum of a couple of hours in each room at the very least, and then there is the expense of all the damage and wear and tear that needs putting right.
If you are dependent on benefits and you get fed up at having such a limited pool of lacklustre properties to choose from, just bear in mind it's because so many landlords have learnt the hard way that to offer anything other than the most basic standard of decor and fixtures and fittings is futile, as they will not get their money back if and when it is trashed.