Buying stamps from retail stamp dealers is a little more expensive than buying from Internet or public auctions, but, in many instances, it is the best method of acquiring stamps for both the serious collector and the philatelist. Retail dealers have a lot of overhead, such as computer and scanning equipment, stockbooks, catalogs, supplies, fees, commissions, and endless hours of labor, in getting their stamps ready for sale. This should be understood, as to why retail sales may cost a little more.
There are stamp dealers all over ... retail shops, private dealers - usually listed in the phone book, dealers at philatelic / stamp exhibitions and bourses, and experienced, full time Internet dealers.
The ideal buying experience would be to talk to a seller face-to-face and to examine the stamps you are interested in buying, before you purchase them. There are very few stamp shops these days, so the best options for this approach are to either make an appointment with a private dealer, or to go to a philatelic / stamp show or bourse. At the bourse, you have the additional opportunity of shopping with a number of different dealers, to get the best price on the particular stamps you are looking for.
There are many experienced, full-time stamp dealers on the Internet, as well. Some have their own specialized web sites, others have online stamp stores, hosted by eBay, bidStart, or Delcampe. I am one of them, and I have also bought stamps for my own collections from many of them around the World. Most of the online stamp dealers use large scans, sometimes of the front and back of the stamp, and they adequately describe what they are selling, as far as catalog number attribution and stamp condition. A FEW WORDS OF CAUTION THOUGH ... I would be hesitant to buy any stamp from an online seller that doesn't have a large scan I can enlarge and examine, or that doesn't have an adequate description.
It is best to pick a dealer that specializes in selling the stamps that you collect. Many honest and experienced dealers have a general knowledge of stamps, but they may not be experts in a particular country, so they may make mistakes in cataloging or pricing. My areas of expertise are in US, European, and European colonies stamps. If I had to sell, say a China specialized collection, I would have a very difficult time of it.
For example, I have participated in Internet auctions for many of the early German States and Switzerland stamps that I have needed. Many times, I have gotten the stamps and found that they were not correctly attributed, especially in respect to perforation varieties, or that they were not in the condition described. Most of the sellers were honest dealers - they just didn't know the specifics of what they were selling. As a result, I have wasted time and money with those purchases. Now, if I want an early Swiss perforation variety or watermark variety, I have found that I save a lot of trouble by buying them from Swiss or German specialty dealers on the Internet. They cost more, especially if I have to pay Euros or Pounds for them, but I do get properly attributed stamps in nice condition, for my added expense.
buyer just needs to educate themselves in their collecting specialty,
and they need to use a little CAUTION when buying stamps online.