Yes a trader that who buys first and second class stamps before a price rise will make a profit.
However the most money is to be made at stamp auctions where boxes full of old mixed stamps can be bought at a very affordable price, these old stamps allow you to make money due to the rise in the price of first and second class over the years, and also on the various other denominations (pence's) as these are undesirable to the stamp collectors who often buy these is bulk and pick out the cream (best ones) to keep for their own collections which results in unwanted stamps with very naff pictures that can be bought very cheaply.
If through business you want people to open the mail you send them (for example) an invoice or a advertisment of the services you offer, a really unusual old stamp will attract their eye and we tempt them to open it - in my experience!!