Products are those items or services that you sell through your website. By default, when your website is first created, a few products are automatically created for you, so you can use them as examples. You will almost certainly need to change the details of these products as part of customizing your website to suit your own requirements.
Our School Pages defaults with a product called "PTA Membership" that is priced at $0.01, so most likely this will be one of the first products that you will need to modify. Using the instructions below, you can modify the price or any of the other details of your products.
Normally only Sales limit need to be set and # of item left should be leave as empty. However the way OSP calculate Sales Limit is by counting of valid order for that product, and if there are still products available user can place an order. It is possible that if there is still 1 product left, and two users place the order at the exact same second, both order will succeed and product is oversold. Given most PTA is not a high traffic site this should be very rare.
If oversold case is totally unacceptable, then the "# of item left" column can be set to prevent that from happening. OSP will decrease the "# of item left" column first in a transaction way so oversold will not happen. However currently when pending orders got abandoned, or user not making payment etc happens, the "# of item left" will not be increased automatically and admin will need to manually increase this number.