The booksellers of early modern Leiden prospered despite being regulated by a guild. In fact, they petitioned for and received permission to set up a guild as late as 1652 when other trades tried to get rid of the tight constraints such an institution imposed (p. 14). For, contrary to a widespread belief among economic historians, traditional guilds helped printers and booksellers in Leiden to adapt to a changing market and thrive. This is ‘The Paradox of Prosperity’ Laura Cruz talks about in her book on the printing scene in early modern Leiden published by Oak Knoll (2009).
The Leiden booksellers survived on an increasingly competitive market because they found a new way to make money in the trade with second-hand books. In particular, they specialised in auctioning the libraries of deceased scholars of which the local university seemed to produce a never-ending supply (p. 57). Their customers were, of course, (foreign) students out for a bargain (p. 222) but also the great and the good who wanted to furnish their libraries with scholarly works (p. 214).