Contrary to former practices he thought professional catalogues good for trade with side-benefits for science as well.

When describing the way of description he suggests that "in this work one must consult more the demands of literature than those of a perfect bibliography.

In this way e.g. a discreet abbreviation of the titles will be desirable, yes, even necessary, while the addition of the publishers and amount of pages may be counted superfluous (in general).

As Muller stated in his bibliography of these prints[2] he first had the intention of publishing a catalogue containing topographical works concerning the Netherlands and its provinces, and pictorial maps of towns and villages, but he abandoned the project because he thought himself not knowledgeable enough in this field.

Not only did he describe his own prints, but also those of other famous collectors like Abraham van Stolk, resulting in the description of 8,443 items.

Meulman and after his death sold to the Gent University Library in Belgium and since then is supplemented by the Vander Haeghen collection of more than 3,000 items.

During his lifetime Muller published 13 antiquarian bookselling and store catalogues relating to geography, voyages and cartography.

[5] Baron von Korff, librarian of the Imperial Library of St. Petersburg, was building the so-called 'Biblioteca Rossica', in which he wanted to include everything printed on the subject of Russia.

Since I began my present business, now more than thirty years ago my firm conviction was, and it has ever remained such - that the antiquarian bookseller can largely serve science - bibliography or literary history especially - without forgetting his own profit; providing his mind be not wholly engrossed by money-making speculations".

In his preface Muller acknowledged the fact that he was able to draw on the collection of Bodel Nijenhuis[8][circular reference].

Muller & Co. had more customers like Baron Von Korff as exemplified by Eino Nivanka's account.

He completed some original editions with facsimiles which, in his own words, "are so admirably executed ... that they will, being printed on old paper, defy the scrutiny of the most skilful investigator".

They specialized in books and prints, but after Muller died, Scheltema began to deal in oil paintings as well, which gained them international recognition as art connoisseurs.