Oh, I know; Gordon trusts the Pattersons and knows they wouldn't steal from him. But theft prevention is not the only reason for a salesperson to go along on the test drive. For one thing, you want someone right there to answer any questions (and to keep putting that subtle pressure on the customer). And there's always the possiblity of an accident; if that happens, you want to know how it happened, not get the customer's version after the fact.
Panel 2: Ooo! It's got a pretty dashboard! And heated seats so Elly will have even more reason to flap her arms! And John is so impressed.
Panel 3: Look at his silhouette. Is that a pout, or what.
Panel 4: I don't get it. Seriously, I don't. Can anyone enlighten me? Does Elly's giant, mutated hand have any relevance?