I also see a lot of items improperly described. For example, if the bowl has dots on the outside its not from the 1950's. That line came out in 1967. I see sets described as primary sets when they have a pale pink one in the mix. As a buyer/collector, you want to get the best item you can for the money. As a seller, you would like to get top dollar for your items. Not everyone can be or wants to be an expert but a little research before listing or buying can go a long way.
In general, the colors of the bowls or casseroles can give you an idea of when they were produced. The 1950's had the famous primary four-bowl set in yellow, green, red and blue. These were all nesting or graduated sized. This same time period also brought turquoise blue (with white or white with turquoise or solids) and two shades of pink. One was a pale, bubble gum pink and the other, called flamingo, is a deeper pink closer to watermelon pink. The 1960's had beiges and blues and all sorts of earth tones. The 1970's was more earth tones and lots of greens. Bowls with clear glass on the bottom are the most recent additions and not quite yet vintage but collectible.
Only Pyrex items are Pyrex. If something has an "F" on the bottom, its not Pyrex but Federal Glass Co. Anchor Hocking is not Pyrex and neither is Fire King. Most Pyrex items are marked. There are a few that are not but they are the exception.
In addition to the standard mixing bowls, Pyrex bowls come in the "cinderella" style - two handles of different sizes that can be used to pour from. There are lidded casseroles that are oval and low or tall and round. There are pie baking pans, utility pans, loaf pans, and "refrigerator" dishes (small rectangles that should have lids but sometimes don't have them). There are measuring cups (worthless without their markings), plates and other dishes. If you find a square bowl with rounded edges it will be the salad bowl and/or smaller serving bowls.
By hand washing your Pyrex, you will keep it intact for many years. Some of the bowls that are more than fifty years old, such as the primary sets, are still in great condition even though they are used often by many families. With a little luck, they will last another fifty years.