I've personally been through this before, and since it came from a manager, your only choice is to challenge him to a duel. First, you'll want to know what this means to him. Some go by old Wild West classical rules. These guys usually turn out to be cheaters. Some go by their own rules, which they typically make up on the spot. However, they're usually honest fighters.
You probably believed that last sentence; they're actually worse cheaters. On the day of the match, dress as goth as possible. The less you look like a good customer, the harder you'll be able to track. Now, this next part is crucial. Even though you know they'll cheat, you have to go by the honest rules and turn to face him when actually instructed. It's vital that you immediately yell "I'D LIKE TO BUY SOME ACCESSORIES." This triggers primitive receptors in his sales brain, launching him into a temporary frenzy in which he cannot distinguish a poodle from an elderly man's ungroomed armpit. Good job. He's vulnerable.
At that point, you must immediately launch into a tirade about poor customer service, dishonesty of sales staff, and be sure to throw in an allegation that he propositioned your mother with a bath tub full of jello and a bottle of astro glide. You may be saying "But my mother is dead!" That's ok, he doesn't know that. It's crucial that you end your verbal barrage with a threat to escalate to corporate. If he looks to parry, quickly shout "phone insurance." One of two things will happen-- the dopamine released by his brain will render him incontinent for a while. For this, you just have to wait it out. Coloring books help. The second is, while rare, much more dangerous. His own self-doubt will render him unable to accept the prospect of the sale, launching him into a frenzy. You must treat him like a bear. Speak in soft tones, but hold your ground. If he starts advancing, thrust your hips in a rhythmic, quick motion towards him. Wide eyes and chants of "Hey baby" are encouraged (but remember, soft tones). These two possibilities lead to the same outcome with a calm demeanor and a good peanut-butter-and-jelly sandwich know how. He's yours.
Politely request that your exchange be honored. Guaranteed to work.