Remaining consistent in person is a challenge, and it is easy to slip. When proofreading, a writer may have more success by visualizing the subject in the focus of a camera. If the subject in focus is the reader or something that belongs to the reader, that is a second person subject. If the subject is something that is not the reader or the writer, it is a third person subject. If the camera starts off the reader, it must stay off the reader, and the reverse is true as well.
Example: “Dogs are sure to love the Top Dog line of crates from XYZ Crates. XYZ offers crates that provide soft padding for a dog’s comfort while also providing strong protection, rated among the best by the Fictional Dog Registry of America. For a great selection of strong and comfortable crates, browse the selection of crates from XYZ Crates.”
This has a shift in person. Where is it? Anyone who said the shift occurred at the last sentence is correct. The paragraph starts in third person (“Dogs”). The sentence continues to reference entities outside of the reader (“a dog’s”, “XYZ”, “Fictional Dog Registry of America”). The last sentence is in imperative (in the independent clause), however. This implies “you” and, as such, is in second person.
This also applies within sentences.
Example: “If you want a great television for your family room, a smart shopper is sure to choose the Master TV from XYZ.”
This is a shift within the sentence. Initially, the subject is the reader (“you”, “your family room”). The sentence then shifts to “a smart shopper”. This is change from second to third person as “a smart shopper” changes the subject from the reader.
Example: “If you want a great television for your family room, choose the Master TV from XYZ.”
This sentence is consistent. It begins with the reader as the subject (“you”, “your family room”), and remains with the reader in the subject by using imperative to start the next clause.