While keeping your profile low at the beginning of TEOTWAWKI  makes perfect sense during the time period if and when the bandits and masses are looting. Once the dust settles, and the survivors begin to recreate a semblance of civilization, then the trading post, and it’s natural evolution, the general store will come into being.
1.) If you are in a remote location, you may not be well-suited to running such an enterprise, but if location permits then consider the benefits of providing this service. Consider also that as a SurvivalBlog reader, you already likely have a base of items from which to start bartering. Bullets, tools, et cetera. Look at your cache and think of what you can barter. You also know what will be valuable before others will. (Chainsaw [gas mixing] oil, hand tools etc.)
2.) By running a trading post and being a central hub, you will have better access to information.
3.) By taking a percentage from both the buyer and seller, you will have an income stream. By this, I do not necessarily mean cash. If someone left 100 pounds of potatoes there to trade and you negotiated a trade with their approval for 50 rounds of 9mm you could take both 10 potatoes and 5 rounds of the ammunition as your fee.
4.) You would have access to a wide variety of items at lower cost,
As time went on, the trading post would become the general store where people brought in their goods, say eggs and chickens and vegetables etc. hand made tools, every day at a negotiated wholesale cost, and you had people that bought them from you at retail.
The following is a quote from Wikipedia:
Trading posts also were places for people to meet and exchange the news of the world or simply the news from their home country (many of the worlds trading posts were places people loved to emigrate to) in a time when not even newspapers existed.
The trading posts in general were of great importance of the history of currency , almost right at the start of trading post history the need occurs to have something as a payment medium, soon trade-tokens and eventually coins were extracted from precious metals like gold, silver and copper for the use of buying and selling goods instead of simply exchange them.
Let us discuss some the challenges associated with running such a venture. You will need
1.) Manual scales for small items (seeds etc.) and heavy ones (bushels of wheat etc…). 1-10 pounds. 10-100 pounds. [JWR Adds: A small precise non-electronic scale for precious metals would also be useful.] Weights of known quantity for calibration and showing your customers you are giving them a square deal.
2.) The ability to provide proper security for you and your customers.
3.) The ability to provide documentation (not easily counterfeited) for people who leave their goods with you for trade.
4.) Perhaps some form of trade-tokens, see above.
5.) The ability to properly store materials, free from insects, rodents and the elements that may degrade them. A solar-powered DC refrigerator might be useful for antibiotics, et cetera.
All in all, if the timing and location were right, running the trading post/general store could be a very rewarding, albeit initially risky venture. – SF in Hawaii