You can learn a lot from booksellers' advertisements. Although scholars often pass by aspects of a book, such as the title page (which typically lists the printer and publisher), the preface, and advertisements, these additions are important in understanding print culture at the time of publication.
The advertisement is especially pertinent for studying the history of the book. Sometimes printed separately in broadsides or in catalogs, advertisements can tell us the price of a work, the format (folio, quarto, octavo, duodecimo), the cost of binding in leather, when it is expected to be completed, and where it can be purchased (among other things).
There are a lot of Jonathan Edwards fanatics these days, thanks to the work performed on him years ago by Perry Miller, as well as the current scholarship of people like George Marsden, Ken Minkema, Doug Sweeney, Gerald McDermott, Michael McClymond, Ava Chamberlain, and others. Edwards had a number of fans during the eighteenth century as well. The New York bookseller and publisher Cornelius Davis (1758?-1831) is one such admirer of Edwards. Take a look at the following advertisement by Davis in a reprinted edition of Edwards's Sinners in the Hands of an Angry God, published by Davis at New York in 1796. Notice, that the advertisement states that Davis takes "great pains" to promote the works of Edwards and his disciples.