Generally I met no tourist traps during 2-week staying around Sao Tome.
Maybe biggest trap is lying in the street deals in the capital, if you like for exmple special cigarrette or beer brand. If you are dealing without local driver or guide, there might be quite a hassle with negotiations and hordes of offerings for the thing you asked. So be calm to get first something similar to desired thing and give money after brief examination and, if you are still without local driver or guide, try to get away *very* from the centre of the circle of zealous sellers.
I think this is the only place in the world, where are no tourist traps(except you pay more than locals for almost everything...).
Best beaches are on the north coast. Praia Micolo(big one), Lagoa Azul(rocky beach, pittorescue) and Praia dos Tamarindos, which is the quiet one and i think the best one.