Hi, we offered on a house back in Dec. After putting in an offer, at asking price, and speaking at the estate agent's request to their mortgage advisors, to confirm we could borrow the amount required, which was confirmed, we heard nothing. Eventually, I contacted the estate agent, who told me that they'd discovered that the 'vendor' didn't actually own the property as he had sold the house, together with the next door house and plot of land behind, to a developer. 
Then in Jan, the same house came on with a different estate agent. By the time I spotted it, they said it had already gone under offer with another buyer. They said the first estate agent was lying, and the vendor had owned it for years. The house disappeared very quickly from Rightmove.
Then last week, I was contacted by the first estate agent. They said the house had been sold and the person selling it was now the legal owner. They said the second estate agent was lying.
They said it was not yet back on the market but they were coming first to us and the other interested buyer, with the property at the same asking price as before - were we still interested? We said yes. They then said the owner was looking for 15K more and it would be going to best and final offers. We offered 15K more. They said our offer was accepted and put this in writing.
Today, I see the property has been relisted on Rightmove at 10K more! I called up and asked WTF was going on! The estate agent's claimed it has been on Rightmove for a week, which I'm pretty sure is not the case. Also claimed the reason it's on for more than we offered is if it was on for less, than any surveyor would downvalue it. They've also said they can't remove it from sale until they have our solicitor details (we're FTBs and so don't have a solicitor we've used before, plus given the dodgy history with this house, we want to make sure we are using a good solicitor; so we haven't provided these yet).
In addition, they've just sprung it on us, we must complete within 28 days! Which seems unlikely to be feasible for a straightforward purchase, which this one isn't. We're not cash buyers and doubt we could get a mortgage that quick if we wanted to - and they never mentioned this previously.
We are in a good position to buy, with no chain and mortgage agreed in principle. So unless they have a cash buyer waiting, don't think their 28 days is likely to happen. But now unsure what else buyer may spring on us - thought we'd agreed a price and no reference to completion date, now it appears they are still marketing the house and want more money and are now suddenly demanding an unachievable completion date. The estate agent also (coincidentally?) sent me details this morning of another property they have for sale, even though they are supposed to be selling us this one!
Any thoughts? Rereading this, it looks like they clearly don't want to sell this property to us. Or is it normal behaviour for vendors?