There's a lot of competition, and I don't know about most shoppers, but I actually could always use more shops in almost any given month. And yes - I could do them all - at least, all the shops that I want (I pass up a lot of shops that I don't want). As you get more experienced, you will learn that many times other shoppers in your area will beat you to the shops that are posted.
Having said that, there's plenty of help here for a new shopper. And guess what - it's all free! You don't have to pay, as you do for Shadow Shopper or JobSlinger Plus, and you don't have to buy a book or a spreadsheet. Everything you find here is FREE, and it's all designed to help a new fellow shopper out. It's set up so that you work at your own pace, reading the things you are most interested in first.
Pull up a chair and read the free information. After reading, set aside some time to set up your mystery shopping business. Spend some time applying with as many companies as you can. Many of the most successful shoppers on the forum are signed up with 150-200 or more. The more companies you apply with, the more assignment opportunities may be available to you. There's a great list below, at the blue link, Official List of Mystery Shopping Companies.
When you apply, you will provide your personal information, SS#, and you may have to provide a writing sample or take some tests. You will sign an Independent Contractor Agreement (ICA), which almost always contains a confidentiality clause (which is the reason that shoppers cannot disclose the names of the clients of mystery shopping companies).