"guarantee the authenticity" is a correct and usable phrase in written English.
You can use it whenever you want to express the idea of ensuring that something is genuine, accurate, or trustworthy. Example: The company hired a team of experts to guarantee the authenticity of their product before releasing it into the market.
Officials at resellers like Stubhub.com, now owned by eBay, guarantee the authenticity of the tickets.
A Groupon spokeswoman said that Groupon did not condone the use of aftermarket sites because the company could not guarantee the authenticity of the Groupons sold there.
On both visits, following precise protocols meant to guarantee the authenticity of the evidence, investigators packed samples of blood, hair, soil and weapons fragments into special containers.
But much more important than "chandelier bidding" is the fact that American auction houses customarily do not guarantee the authenticity of what they sell.
Part of the case, for example, is based on a California law that requires dealers to guarantee the authenticity of the sports memorabilia they sell.
News gathering takes time, energy, courage, people, humility, creativity and layers of editorial oversight to guarantee the authenticity of the final product.
Finally, Park West guarantees the authenticity of every work of art it sells.
Costco guarantees the authenticity and perfect condition of the art and, unlike many galleries, will accept returns.
The Grams are a group of unimpeachable integrity led by the lugubrious Keva (Liam Boyle), whose abusive childhood guarantees the authenticity of his music.
A blockchain is the technology that guarantees the authenticity of an online currency by creating publicly available "ledgers" of transactions in blocks of data.
Artnet.com, for example, says that "All lots have been vetted by reputable dealers and compared with existing auction results," while Sotheby's guarantees the authenticity of works it sells online.
