At flea markets and/or garage sales for good ssources, be prepared to buy. Carry enough cash with you. Have between $500/$1,000. Do not carry this amount of cash on you all the time; only when scouting for merchandise, Take a large enough car or truck so you can take a deal should you find it. Be prepared and plan ahead. It will save you time and money.
Know your prices ahead of time. It is very important. Write up a cheat cheat or list with prices you pay so you never get cheated on a deal. Buy the entire deal if it meets your needs and the price is right. Even if you save only 20% from what you normally pay that is more profit in your pocket. Remember to buy low and sell high, but sell your items at a lesser price that any retail store. This is a win-win situation for you.
This is your business; why not make a high profit. But keep your mouth shut on what and where you buy what. That information is extremely valuable.