When "Sonya" uses her real voice, it is provided by June Foray, the voice of Rocky the Squirrel and Natasha Fatale in the Bullwinkle Show.
Max mentioning that people keep asking if he and Larabee are related is an inside joke, as Don Adams and Robert Karvelas were cousins in real life.
The KAOS furniture store where 99 is held captive is named Melnick's Furniture Warehouse, after Daniel Melnick, a partner in Talent Associates, Get Smart's production company. A season two episode also featured a KAOS pet store run by Melnick, "The Smiling Killer".
Up to this point, Max and 99 have not had a phone upstairs. The story begins with 99 talking on a bedside phone, and there is talk about listening on the extension.
The title has a very clever double meaning. The first is obvious on the Agent 99 and her impostor. But it also refers to any advertisement trying to sell a product with the usual 99 cents added, to make it appear much cheaper than the next-highest dollar rounded amount. In this case, 2 dollars and 99 cents sounds like a bargain to pay instead of exactly 3 dollars. A very old and commonly-used advertising trick.