Here is the problem with looking at a mark in isolation:
It is like looking at one eye, and finding another, and, on the basis of finding a similar or possibly identical eye, identifying the face.
It is not to rule out that the teapot
is sterling, and
by J. Reid. It is that, looking at all the marks that are present, they do not suggest sterling (tho a jeweller can test it for you) and they do not suggest J. Reid - unless J Reid had a really bad day, or was sloppy and forgot to have the teapot assayed etc. etc.
The best way to proceed, Sam, is this:
take the teapot to a reputable jeweller and ask him to test it for silver content. It might be sterling but one would not say so, given the marks. You can also send a copy of the picture to The Edinburgh Museum, 142 Canongate, Royal Mile. (Tel: 0131 529 4143), or you could contact the Edinburgh Assay Office
Edinburgh Assay Office
Goldsmiths' Hall
24 Broughton Street
Telephone 0131 556 1144
mail@assay-office.co.uk
As for buying on line:
IF you should think of buying from an auction website, first of all ask for the hallmarks and verify that they represent properly marked sterling.
As soon as you receive the item,
have it tested!
At least that way if it is not what you thought you bought you can get your money back.