Working roughly chronologically here is an ink stamp from Bland's.
This stamp shows Bland's address from approximately 1885.
Hamley's later bought out Bland's but here is a label from one of Hamley's other shops from before the takeover, 229 High Holborn.
In this 1893 edition, the label has been used to cover up the publisher's printed address. This common trick is used to try and ensure the customer returns to the magic shop for more books instead of buying direct from the publisher. The catalogue page has also been pasted in the book and wasn't part of the original binding.
This paper label is later and was found in a copy of Hoffmann's Latest Magic, so it's probably from 1918.
Later again is this purple ink stamp found in Percy Naldrett's 1925 book Volume Six.
Another big dealer during this period was the department store A. W. Gamage. They often put small paper labels in the inside covers of books. The one below is from a 1904 edition of Hopkins' Twentieth Century Magic.
In 1905 Will Goldston began managing Gamages' conjuring department. Here's a label from around 1910, during Goldston's time there.
Goldston left Gamages in 1914 to establish his own magic shop. This 1917 edition of Supplementary Magic by Elbiquet contains one of Goldston's paper labels.
Looking at a much smaller dealer now here's a stamp from a 1909 edition of Some Modern Conjuring by Donald Holmes.
I'm not familiar with Maddock, mentions of him are scarce. According to Genii's Magicpedia his real name was Jas. W. Bell and Fergus Roy mentions him as a relatively large dealer in The Davenport Story, Vol. 1.
Speaking of the Davenports, their labels crop up very often, particularly their seal-like paper labels. In this example a solid ink stamp has been used alongside the seal to discourage customers from buying direct from Burling Hull.
This seal is perhaps the most common, and shows the 15 New Oxford Street address they held between 1915 and 1937 (for a list of Davenports' addresses and when they used them see the FAQ section on the Davenport Collection website).
Here is a clearer view of a similar seal.
There are also at least two gold versions of this seal. This one shows their address from 1938 to 1942.
This label wasn't from a book, but from the inside lid of a Sand and Sugar can.
They also produced a gold label with no address on, instead it simply had Made in England written around the edge.
This label was found pasted in a book from 1945. Often, and understandably, some magicians weren't best pleased with having labels pasted in their new books so it's not uncommon to see evidence of their removal.
Of course many dealers sold second hand books and fixed their labels in many years after the book's publication. Here's one such example.
The famous escapologist Murray sold magic items and jokes after poor health prevented him from performing.
I'm aiming to add more labels and stamps to this post as I find them. I've just picked a few books from my library, as I come across more I'll add them to the list.