English equivalent for the Chinese idiom "to pass off fish eyes for pearls"

Question

Are there any (general) English equivalent for the Chinese idiom 鱼目混珠 (to pass off fish eyes for pearls) which basically means to pretend something fake is real? IE:

1. To try and pretend to be someone else
2. To pass off fake products as genuine

Answer 1

For sense #1 and #2 we have the idioms/phrasal verbs

palm (oneself) off as

To pretend to be (someone one is not) m-w

palm something off, palm off something

Sell or dispose of something by misrepresentation or fraud.

palm someone off, palm off someone informal Persuade someone to accept something by deception. Lexico

pass (someone or something) off as

To cause people to wrongly believe that someone or something is someone or something else

amateurs passing themselves off as professionals m-w

---

When someone is duped (your sense #2), we in the U.S. sometimes say they were sold a bill of goods

Something intentionally misrepresented: something passed off in a deception or fraud—often used in the phrase sell a bill of goods m-w

Originally and chiefly U.S. a consignment of merchandise; so in colloquial phrase to sell (someone) a bill of goods: to persuade (someone) to accept something undesirable; to swindle. (OED)

---

A rather dated U.S. idiom, still heard once in a while as jocular advice to guard against being duped (sense #2), is

don't take any wooden nickels

Take care and, specifically, try not to get swindled. The phrase is thought to have originated in the early 20th century when country residents visiting the city were considered easily duped. Primarily heard in US. Farlex Dictionary of Idioms

Protect yourself (against fraud, loss, and so on). This warning against counterfeit coins dates from about 1900 and is distinctly American in origin, the nickel being a U.S. or Canadian five-cent coin. Why a wooden coin was selected is not known. Presumably making coins of wood would always have been more expensive than the intrinsic value of metal coins. Several writers suggest it replaced don’t take any wooden nutmegs, a now obsolete saying dating from colonial times when sharp traders sold wooden nutmegs mixed in with the real spice. In print the expression is found in Ring Lardner’s story, The Real Dope (1919), “In the mean wile—until we meet again—don’t take no wood nickles [sic] and don’t get impatient and be a good girlie.” Christine Ammer; The Dictionary of Clichés at theFreeDictionary.com

Answer 2

Perhaps rather old-fashioned now is the idiom sell someone a pup.

From Wiktionary:

• sell someone a pup (UK)

To sell something of little worth, pretending that it is something else of greater value.

From an old swindle, where one would be sold a bag purportedly containing a piglet, but actually containing a puppy. Compare pig in a poke.