So I can understand that if a company wants their staff to be shopped, they can tell their employees ahead of time that their calls may be recorded so staff are aware. However, if you’re shopping the competition, how is it okay to record the calls since the competitors staff are not aware?

Most of your post is filled with inaccuracies. For starters the whole concept depends on what state you are in. There are 12 two party states where all members of a conversation have to consent to a conversation being recorded. If you are talking about one of those 12 states then the company can't "tell" their employees their calls may be recorded. The company has to receive "consent", which is quite different from "telling". Usually this is done by having them sign a consent form when they are hired. In those cases, the company ALSO has to have consent from the other side of the conversation. So if you are in California (a two party state) and Griffin's Widgets decides they want to record their employee's phone calls, they ALSO have to get consent from the person they are talking to. This is normally done by a recording played at the beginning of the call prior to a customer being connected to an employee. I'm sure you've heard them. "This call may be recorded or monitored for whatever purpose blah blah blah" The tricky thing is, this also gives the customer the right to record the conversation since at that point both parties have consented to being recorded.

So, here are the possibilities:

1. The person being recorded is in a single party state - no worries, completely legal
2. The person being recorded is in a two party state and there's one of those lovely this call may be monitored or recorded notices before they answer - no worries, you have both consented to being recorded
3. The person being recorded is in a two party state and the employer has had them sign a consent form and the shop is being done by the employer - no worries, they have received consent from the employee
4. The person being recorded is in a two party state and this is a competitor shop and there is no notice at the beginning of the call - oooooops you have possibly committed a crime.

For the record the 12 two party states are:

California
Connecticut
Florida
Illinois
Maryland
Massachusetts
Michigan
Montana
Nevada
New Hampshire
Pennsylvania
Washington

Notice also that I said "possibly" committed a crime. There are other circumstances that affect it. If the recording system plays a beep periodically during the conversation that is considered notification of recording, which also legally constitutes consent. Also if you take away the expectation of privacy there are arguments this also takes away the need for consent. For instance if you call from a crowded mall on speakerphone.

bg has given an admirable account of the possibilities and issues. One caveat; out of an abundance of caution, many treat Delaware as a two party state.

Michigan is often listed as a two-party state but, in fact, does not have a statute on the books prohibiting the recording of a call to which only one party has given consent. It DOES have a wiretapping statute, which prohibits calls being recorded when neither party has given consent. This is not to say that it is OK to record as if it were a one party state, but there is nothing prohibiting it, either. There have been lawsuits involving one party recording without the other party's consent and generally they have been resolved in favor of the party doing the recording. But, since this is not specifically addressed by statute, it is best to be extra cautious when recording without the other party's consent in the state of Michigan.

One more thing to consider. Do not assume that just because you are dialing an area code that is a one party consent state that the person who answers is in that state. The call might be forwarded to a call center in a two party consent state. Some call centers are overseas, and many countries (all of the EU) have very strict privacy laws.

I've never worried about recording anyone, one or two states.