Rois, as somebody who's looking at the houses at the moment I can tell you how I am looking at it - having spent a couple of years in a rented accommodation which was basically brand new when we moved in and a "fine example" of how bad the quality of construction works was on the new estates which have mushroomed around Ireland in the last ten years, I am really paranoid about seeing any water marks. We've had some serious problems with our bathrooms in all the properties we've been renting - all of them were leaking. I could bet I can spot a repainted ceiling or any even ancient water mark at midnight with my eyes closed. When viewing the properties, we've been looking at the bathrooms, knocked at the tiles to find out if they were loose, automatically discarded all houses with a mouldy smell in the ensuits and bathrooms and thoroughly checked the floor and the insulation round the tube and the shower area. Scratch marks on a wooden floor are normal when the house has been inhabited and I wouldn't really bother as it can be fixed easily. A leaking bathroom however is very costly and annoying.
That said, if the water mark was a result of a leaking bathroom, have the bathroom fixed, resand the area with the spot and, if asked, tell the buyer that work was done on the bathroom /you might even want to show the invoice from the plumber or tiler with the description of what was done/. Now this might sound too picky but this is a buyer's market and if people don't like a property, there is plenty of others to view.
Luckily, you are the owner living in the house because any previously rented property would be a no go for me as well. Personal items - they actually give the house a nice character - I was in a house with china dolls and garden dwarfs and actually found the house really nice and welcoming because combined with the family photographs and the furniture it gave the impression that people liked the house.
No smoking in the house as the smell will always be there - if you are a non-smoker, like me, it's annoying as hell.
Likewise, if you have carpets, don't try cleaning them just before the viewing - you might not have the time to air them properly and the smell from a wet carpet is worse than that of a whole pack of wet labradors who just bathed in a dirty pond.
Use some nice deo but don't overdo it because people might think you are trying to cover up for something smelly.
Now, I love dogs and cats and just any furry pet /no tarantulas please, though/ so if I see a food dish or a pet's toy, I tend to like the house more. There might be however, some people with serious allergies coming to your house or hygiene freaks who equal a pet with medieval pestilence so clean the house, put the toys and food dishes and any other pet related items away when expecting viewers.
Likewise - keep the house tidy and if you use any of the rooms as an additional storage room /and it's not a storage area/, clean the clutter away, put it in a shed or in the attic. Normally, people wouldn't check the attic during the viewing so might store whatever you want there /unless it's not making any funny noises or it's not smelly/. I viewed a house which was supposed to be a 4-bedroom house but one the "bedrooms" was used as a storage room and I found it extremely off-putting.
Hope I helped you to show the buyer's perspective - neither me nor my partner have any real DIY skills so we tend to be extremely picky about the state the house is in and any potential repairs as we would have to get somebody to fix it for us, meaning additional expense.
