Cant tell much more from the description on ebay. Being from the US is a good thing, and I dont recall hearing anything negative about the seller. The clincher should be the weight. The seller claims they are pieces of eight. If they are 8 reales, they should weigh in between 23 and 26 grams each. The higher number for a good specimen, the lower number will take into account weight lost due to corrosion and cleaning. For a 4-reale, cut the 26 gram figure in half, and follow that formula for a 2, 1 and 1/2 reale. I am not seeing any "seems" around the edges, so that is a good sign. Is the pitting in the metal more natural and sharp or does it appear to be more rounded or soft. If the later, could be casted and in that case, replica.
Alos, how do they sound when they dropped on a table top? Heavy "thud" like solid silver, or a more higher pitched "tinney" sound? If the "tinney" sound, you have a good chance at havng replica's. If they are replica's, they are good ones. If they are real, a GRET buy at $55.00.