The house we're buying went on the market at £265,000. We put an offer in at £249,999 and the vendor flatly refused (he had previously refused an offer of this amount).
Our original limit was £250,000, but we were so sure of this house (great for us as a family, but when it's just us, accommodation is very flexible for living downstairs, so could be a home for life. Also, close to all local services, friends and it's in an area we love) . Given that it could be a home for life, we decided to put an extra £10,000 into the pot (to cover stamp duty) and offered £254,000. Vendor came back and said it was ours for £255,000.
We are lucky in that the property is in immaculate condition, nothing needs to be done other than a new shed, cat flap and changing the garden, so we didn't have to budget for major changes in the first couple of years.
I think if you have a property close to the stamp duty threshold, then people are going to try and offer immediately below the threshold. We didn't like the thought of paying all that extra tax, but also it impacted on us greatly as we had to pay £5,000 we hadn't budgeted for.