1 amp per strip sounds high. If you have a multimeter, you might check this yourself and see. But if the seller says 1 amp, he is more likely correct than I am. It would be instructive to get a 12v power supply that supplies more than 1a and measure the amperage that the strip draws.
I have no personal experience, but have read that, generally speaking, it is not good practice to put LED strings in parallel because one burning out can put other strings over their limits if they are not properly protected by fuses. This may not be a problem for this type of string or power supply - someone more expert than I am needs to weigh in. When I asked about the effects of running 5050 LED strips at 12 volts but below their rated amp draw (e.g., 0.5a per strip in your case), I was told this will cause the power supply to run hot and perhaps overheat. In contrast, proving too much current was said not to be an issue. For the most part, I try to match the amps supplied by the power supply with the requirements of the string and add ~10%. I only use them in my stands and under cabinets.
