Ha ha, I thought my buyer was bad, but yours is crazy! I'll tell you what mine did, might make you feel a bit better.
We were a bit cautious of her from the start. She complained that she had to view at the same time as another couple as it 'spoilt her house buying experience.' Anyway after being on the market 9 days we had three people making offers and hers came out top.
So we went with her and for a week or so everything was fine, then she kept wanting to visit the house for different reasons. To show various distant relatives around, to measure for sofas, to compare wallpaper samples to the carpets and to then ask for an offcut off carpet so she could use it to colour match decorations / furniture. We were very accommodating and never refused, even though I'm very pregnant and had to take the dogs out every time she wanted to come around. Anyway - she got a survey done and it highlighted two non essential items of work. One was clearing moss off the roof (just a small amount on all houses in street because of the way they face) and the other was to straighten a leaning drystone garden wall - which has lent since we moved in 4 years ago. Due to their frequent visits we were able to ask buyer about these 'issues' directly and her Dad turned up with a builder at 8 am one morning (without warning) to look at the roof problems. Her Dad and builder said the roof work was minimal and they would cover the cost as no evidence of damp inside etc (house is only 13 years old). He said he would be back the next day to look at the wall with a different builder. We left back gate open so he could do this. After this we heard nothing for two weeks. We kept asking for updates from them via the EA and they came back as, oh the work is minimal they are just waiting for quotes. When her Mum came to pick up an offcut of the carpet we asked her and she again said, oh yeah the work is minimal and we are just waiting for quotes. Now in this time we had told our purchasing solicitor to put a hold on the process but because of what we were told by them and it being 'minimal' work we told our solicitor to proceed again and paid out £800 for valuation and survey on our house that we were buying. When her Mum visited she directly asked about how far into the buying process we were with our house and if we would be ready to complete the sale soon.
A couple of days later our selling solicitors sent all contracts through for us to sign and we presumed everything was all go. A few days later our EA calls us saying the buyer wants £10600 off the price of the house and was refusing to sign her contract until we agreed to that (to put it in perspective the house was sold for £115700.). She had a quote of £1600 for new guttering (even though the homebuyers report specifically said the issue was with moss) and £9000 for a new wall and fence on the top. We had got some quotes for the wall work when they first mentioned it and ours came in at £1500-3000 so we were more than a little shocked (as was our EA.) Anyway we went back to her saying no way, especially as since our house had sold two exact same ones had gone up on the street for £10,000 more than ours. We offered a maximum of £1500 off the sale value of the house to continue with the sale or we would put it back on the market for more and get the work done ourselves,
She said it wasn't enough so we put it back on the market the next day, it was sold 6 days later for more than she paid and we've since had the work on the wall done ourselves for quotes we had. The best bit was her Dad stopped to talk to the builders who were working on our wall and was quizzing them about how expensive it was etc.
If I ever sold again I'd definitely avoid the awkward ones from the start. We think she planned to ask for this money off last minute, she knew we were keen to move before the baby arrived and thought she could force us into having to lower the price. All the way through the sale they had dealt with my very nice and accommodating husband but when that quote came back I (crazy, hormonal and pregnant) was the one who wrote her the email basically telling her to sod off and stop taking the piss. I'm guessing up until that point she had expected us just to roll over and say yes. Anyways all being well our sale/purchase completes on Monday and hopefully the baby will stay put until then :-)