Buying a Barometer —
and what to watch out for:
Check if the case and fittings are well made, test if the marker hand is not too tight, neither too loose. Much more on the technical side you cannot do and have to rely on the shop owner / sales assistant. If they do not ask you where the barometer will be used, e.g. in your town by the sea or at some other place at a high altitude, then just walk out of the shop, because they do not know the first thing about these goods they stock.
Most barometers of the aneroid type have altitude ranges of about 1000 meters. At coastal areas and inland up to 1000m one would use the models with the lower range. At the higher altitudes the 1000m to 2000m units come into use. On some models I can exchange the movements to suit your altitude.