Biography
You're in a sticky situation; you need to get something and there doesn't seem to be a cheap or legal way of getting it. (It could be banned, rationed, expensive, from overseas or possibly just made in extremely limited quantities). If you're unlucky, you'll have to visit Honest John's Dealership. While this trope focuses on used cars, it covers anything sketchy that a pushy salesperson tries to sell you.
These are the guys who'll attempt to sell you anything, mostly items that Fell Off the Back of a Truck. The items may be off warranty, withdrawn by the manufacturer in your country, returned items that broke and got refurbished, salvaged from a wreck, or out-of-date models. The "gently used car" was probably an Uber or police car. They sell anything that is just barely legal. The prices are usually dodgy too, either Too Good to Be True or obnoxiously overpriced. (The former usually catches more people out than the latter.) Sometimes there's big hidden fees and charges. Sometimes, there's a catch hidden on page 26 of the agreement. All in all, their main goal is quick money.
Like its cousin trope, the Friend in the Black Market, Honest John can fit anywhere on the neutral or chaotic side of the Character Alignment spectrum: a good comparison would be the Loveable Rogue Jerk with a Heart of Gold 'Del Boy' Trotter or Mr. CMOT Dibbler types VS Jerkasses like Mr. Wormwood or Sociopaths like Harry Lime. After all, selling malfunctioning blow-up dolls is a far more forgivable occupation than selling The Alleged Car that hates you with a passion or fake pharmaceuticals to orphanages. If the "Honest John" character is genuine, pure evil, then you've got a Deal with the Devil on your hands. More likely he's just a Slimeball - maybe one with friends in the Totally Not a Criminal Front. However you slice it, you're probably not coming out ahead on this deal.
Expect him to wear an obnoxious outfit (plaid polyester suit jackets seem to be popular), record Insane Proprietor advertisements and Kitschy Local Commercials, and say "But Wait, There's More!" every other sentence. If this character is rendered as a Funny Animal, chances are quite high that he'll be a weasel or a fox. Items for sale at Honest John's may include All-Natural Snake Oil, Asbestos-Free Cereal, the Brooklyn Bridge, and of course The Alleged Car. If he's primarily out to scam women out of their money rather than everyone, then he's a Sexist Used Car Salesman.
Despite trying to appear as having Names to Trust Immediately, chances are fairly good that the "Honest" part makes it an Ironic Name in the same spirit as the People's Republic of Tyranny. You know, if he has to tell everyone he's honest...
Compare and Contrast Friend in the Black Market, who also sells items at a premium but at least guarantees he's giving you the good stuff. May also overlap with a Shady Scalper, who generally will gain the items they sell legally, but in doing so inflate the prices to profit. In a military setting, this trope is almost guaranteed to overlap with The Scrounger. See also Snake Oil Salesman, Shady Real Estate Agent, New Job as the Plot Demands, Crooked Contractor, Medicine Show, The Barnum, and Traveling Salesman. Only tangentially related to Richard Nixon, the Used Car Salesman, as that doesn't actually require characters to have this job, just a different one than in real life. Related to Unknowingly Possessing Stolen Goods, where a character gets in possession of items that are stolen, which can be sold from one of these dealers.
Completely straight examples tend not to last long in Real Life, but we've probably all met one at least once. They're called "gray market salesmen" in business/econ terms. Ironically enough, they have less of a reason to lie and cheat than new car salesmen, as used car sales are a) more profitable in general and b) usually grant more consistent commissions because you're largely just selling the car and have fewer middle-men to appease, while new car salesmen derive a far larger portion of their commissions from tacked-on extras, leading to overwhelmingly high-pressure tactics and occasionally outright lying or grossly stretching the truth.