I am confused as to the actual size of a 1/4 sheet cake. Some have told me 9x13 and then another store tells me that it is a smaller pan 7 by 11. I am starting to get cake requests and will feel very silly if I don't know the right size of a cake or how many it serves

Not a silly question at all! I always go with a 9x13 for 1/4, and 12x18 for the half. I also have the 8x11 pan, which is a wonderful size for a single cake mix. The bakery standards are slightly different, though. One by my house uses a 12x16 as their half sheet, for instance. When people ask for a certain size, it's best to ask them for how many servings they want. I can't tell you how many times my MIL asks for a half sheet, when all she really needs is the 9x13!