Professional Princess
Princess, Princess, my love, this is way too harsh and not fair on the OP.
Lots of solicitors use stamps of the type described, simply because it saves having to write out the sentence endless times. The stamp, however, is meaningless unless the solicitor (or other authorised person) has also signed the page, and added his or her full name, business address, qualification (eg solicitor) and the date. I dunno where most solicitors get the stamps from. I've never bothered to ask. It is easy enough to get a rubber stamp custom-made though, and quite likely the Law Stationers also sell them if one looks at their catalogues. It doesn't make a jot of difference who owns the stamp. If the documents have been pre-stamped, the solicitor or whoever will simply be grateful that the person concerned has been considerate enough to save the signatory some time and effort.
However, where solicitors bother to use a stamp, there is merit in leaving it to them to use their own, because the stamp usually includes the name and address of the firm as well, making for even fewer words that have to be scrawled out in longhand. If they haven't saved themselves time by investing in a custom-made stamp, presumably the place is stuffed with solicitors who don't mind wasting hours of their time for no good reason at all.
Best regards
Gill Palmer