You will need
- - catalogue of postage stamps (whole world or the specific country you are interested in);
- - access to e-resources, devoted to philately and collecting;
- live consultation of an experienced philatelist.
Find the catalogue of postage stamps can be purchased or even borrowed from the library. Large foreign catalogs are expensive in the open market they are hard to find, but the catalog of stamps of the USSR found in many secondhand stores. Therefore, if the brand, the price of which you are interested in, released in Russia in the Soviet era, to understand you will be a lot easier with the brand-revolutionary or foreign. Don't take these prices for the brand literally just try to sort out the values of the brand and comparing its price to the average cost of other stamps of the same time.
Search the Internet specialized sites and forums stamp collectors (or collectors in General, among whom philatelists certainly there). Many such resources have the same directories in electronic form, and there is also the possibility of not showing himself to discuss the alleged value of the rarity with experienced philatelists - and it is definitely worth taking advantage of.
Find out if there is a stamp club in your city. If so, where it is located. If you come to the connoisseurs and lovers of stamps with your copy and ask them to give a rough information about it for you to anything does not oblige. The opinion of one individual collector, should not be taken literally - match insight on the potential value of the franking method, talking at different times with several experienced philatelists.
Try to assess the condition of the stamps, the possible market price which you are interested in. Remember that the real value of a collector's item, including postage, is highly dependent on its condition - degree of preservation. Philatelists necessarily take into account the presence of all teeth, clear cancellation (if the brand was mail) or the presence of glue on the reverse side (if mark was not used on purpose).