This is a pretty piano, and it's good to see that it has retained all its brasswork and green inner-board. It's numbers are 10445 (ink) and 8791 (stamped) dating it to 1811 or possibly 1812.
The seller writes:
I bought the piano to form part of my Musitiquity project looking into the domestic music making of the Regency period and in particular using the music books of the Austen family as a source. It was invaluable to practice on a period instrument and it has taught me so much more about the music written at the time and how it should be played. It gave me the confidence then to take Musitiquity 'on the road' performing at National Trust properties and historic houses, some of whom have their own square pianos like the Jane Austen Museum at Chawton.Tuning instability is the only reason I changed instrument because I want to now take the instrument on the road with me too. Something later and more stable like the Broadwood was the ideal answer. I definitely feel that since some strings stay tuned far less readily than others that is is wrestplank wear rather than some overall structural fault.
Some restoration was done about ten years ago, when the instrument was given a complete and authentic set of new strings, and the felt hammer-covers from earlier work replaced with appropriate leather. The tuning instability has only developed within the last few years, and it seems likely that this is the result of the piano's move from an unheated barn (where the restoration was done) to a modern centrally-heated environment, with consequent drying-out and shrinkage. Since this affects only some of the notes, it seems likely that the problem is due to loose tuning-pins, rather than any major structural issues.
A leading restorer has examined the piano and suggested that there is a good chance that bushing about a third of the tuning pins would solve the problem. This is a job that could be undertaken by a careful amateur: it involves drilling out the hole to perhaps 8 mm, inserting a beech dowel, and centre-punching and re-drilling this to make a hole to fit the pin tightly. Friends of Square Pianos will be happy to offer more detailed advice.