I'll leave others to the price elements, but:
Pics 1 and 2: The front is ugly! Strangely, if I've got the right house (which I think I have), it looks better on streetview - did they rip out the front garden? All of the neighbours look much nicer. They need to replace the gravel with something not so...grey and get some plants in there, preferably a non-gravel path leading to the front door (gravel, heels...) and some plants.
Livingroom: Get rid of the brown wall, it's a really unpleasant shade. I can normally see past decor but that particular colour is very unfortunate. I'd be tempted to try a shuffle of the furniture as that sofa under the window looks wedged in and makes the room look small, whereas I suspect it's actually giant DFS sofa-syndrome (why are those things so enormous btw!). The ceiling lights are very dated and ugly, and the textured ceiling is pretty offputting so it would be worth getting it skimmed (or stripped if it's just paper) and getting some modern lighting in there too.
Dining room: Rearrange, move the table so it's in the middle of the room rather than being a focus. Move the fishtank out for the photos too. I'd also repaint the goldy coloured wall to match the others. Same issue as livingroom re ceiling and lights
Kitchen: Pretty much fine, although strip lights are pretty ugly and tend to give off a very nasty shade of light and again with the textured ceilings. A multi spotlight bar or similar would look a lot better
Conservatory: just looks like a dumping ground. Don't suppose it's big enough to house the fish tank and the giant sofa?!
Photo 12 (pink and purple room) - now, these are all colours I like but NOT IN THE SAME ROOM with a giant black bed. A dark carpet especially might well put people off, but I think if the room was otherwise toned down it might help. Maybe get rid of the pink wall, paint it lilac to match the bedroom and get some nicer, floor length and not so skinny, cream curtains to make the window look nicer. Plus a mirror or picture over the bed, again light and bright
Photo 13 (and 17) - it's a cream box, put some nicer bedding on it and straighten the lampshade and it would be ok. And take down the clothes hanging on the wall, it suggests storage issues.
Photo 14 - bathroom; agree with others about the colour scheme, the mix of golds and greys isn't great. Painting the walls white would probably tone down the effect though. It's also a dreadful photo which needs to be retaken by someone with a clue; when they're doing that they should take the baskets off the windowsill, the pink washer off the bath and the blue "Baths" ornament out - everyone knows what the room is for!
PIcture 15: Nuke it. Alternatively, paint it cream, take the chair out, put a small bedside in and hang some curtains. And lose the pink lightshade
Picture 16: I don't like the wallpaper but it's at least light and bright so less bothered by changing it, but the treadmill needs to come out and a bed needs to go in as it currently looks like a dumping room which created concerns about storage (especially combined with the conservatory dumping ground)
Garden: A few plants wouldn't go a miss, but it's not offensive and I don't think would put people off as such - but it's a good size and could be a selling point if done better.
And, for the love of god, lose the bloody wicker hearts everywhere :D