Yes, whitening teeth can be very predictable. You can try over the counter products and see what success you have with them. I prefer to make my patients custom trays and supply them with an appropriate teeth whitening product. People using custom trays get better and faster results because they are easy to use, especially compared to some over the counter products. Custom trays are very cost effective compared to in office dental bleaching.
Products like Zoom have great marketing, but the results are no better than custom trays. Also in office bleaching tends to be expensive because dental chair time is used, and who likes feeling like being under a heat light in a diner? Go for custom trays and at home bleaching and you will be very pleased with the results.