Before buying, you need to know the value of the artists or objects you are interested in. It will help you determine your price on auction day. In practice, there are many sources of information.
For drawings, paintings, sculptures and regular market studies, the artprice.com website is absolutely indispensable. By paying a minimum subscription of 148 euros per year, it gives you all the sales results of the artist of your choice. If you want to go further and have information on all sales in the world and access biographies of artists, the subscription goes up to 178.20 euros. Finally, it goes up to 268,20 euros and you will then have access to all the other data of Artprice like the indices and the updated prices of the works.
There is also a smartphone subscription of 99 euros to access the artists' rating. You can also subscribe to Arnet.fr. The annual subscription varies between 225 euros and 326 euros.
For furniture and art objects, research is more difficult. You can consult auction.fr or the website of the Gazette of the hotel Drouot, provided you subscribe for 105 euros per year. If you content yourself with Gazette which also comments on the results of many sales, it will cost you 100 euros.
Also note that most sales companies have their own site on which they publish the results of their different vacations. This is the case of Sotheby's, Christie's, Artcurial, Piasa, Tajan, Pierre Bergé, Millon ... Of course, you should know that the chest of drawers you were looking for was sold by one of these houses. This forces you to have the Gazette.
Finally, many dictionaries publish results every year. Among the best known are ArtPrice Annual, a paper version of the website, the Guidargus of painting or furniture, or the Valentine's argus, which cover the most diverse domains (sculptures, silverware, ceramics, paintings, archeology, etc.).