The Dosi were a humanoid civilization native to a world in the Gamma Quadrant. The Dosi placed great importance on business and were extremely aggressive negotiators, to the point that fatalities were not uncommon.
The Ferengi, represented by Quark and Pel, negotiated with the Dosi in 2370 to purchase 100,000 vats of tulaberry wine. When the Dosi were unable to fulfill the demand, they referred the Ferengi to the Karemma, an important member of the Dominion. (DS9: "Rules of Acquisition")
Food and beverages
According to the script for DS9: "Body Parts", this species' name was pronounced as "DOE-zi".  In a cut line from this story, Rom listed the Dosi as having individuals who Quark had acquired debts with.
According to Star Trek: Star Charts (pp. 70 & 71), the Dosi were from the planet Dosi which was located in the Dosi system. The homeworld of the Dosi was a Class M world. The official name for their government was the Dosi Confederation, which governed the planet from the capital city of Relxer-D. The dominant species on the planet was the humanoid Dosi. In 2378, there were an estimated 1.5 billion Dosi living on the planet. In the late 23rd century, the Dosi established trade relations with the Vorta. The planet Dosi was discovered as a result of the Gamma Quadrant Bio-Survey. Dosi system primary was a Class M star, with a magnitude of +9.
In "Rules of Acquisition", Quark states "He (Zek) never wanted to do business with the Dosi. He just wanted to use them to get to a more important member of the Dominion." Although we cannot be certain, this might indicate that the Dosi are a member of the Dominion themselves, albeit a less important one.
A later statement by Ronald D. Moore, however, might cast the Dosi being full members into doubt (although he was not necessarily referring to the Dosi): "There are other races in the [Gamma Quadrant] that are not part of the Dominion and the Ferengi at least have established trade with some of them." (AOL chat, 1997)
It was director David Livingston who opted to give the Dosi bright red face make-up. This was inspired by a book of African tribal face paint markings. (Star Trek: Deep Space Nine Companion (p. 97)) According to Michael Westmore, the make-up designer for the Dosi, their facial art designs were specifically based on colorations found in tribes in Borneo and in the South Seas. (Michael Westmore's Aliens: Season Two, DS9 Season 2 DVD, Special Features)
Proceeding from how the Dosi had been conceived, David Livingston tried to make them seem comical. "The Dosi were written kind of silly," he remembered, "so I ended up directing them kind of silly [....] The Dosi were described to me as very 'buff' men and women, so that's the kind of actors we chose." (Star Trek: Deep Space Nine Companion (p. 97))
Ira Steven Behr was dissatisfied with the Dosi. "I didn't particularly care for the Dosi on a lot of levels," he critiqued. "This was the first [gamma quadrant] race and no one knew what the hell it was going to look like." (Cinefantastique, Vol. 25/26, No. 6/1, p. 100) Michael Piller felt likewise, believing their makeup and headdresses were too elaborate to look credible. However, David Livingston's opinion differed. "I personally felt that in 'Rules of Acquisition' these aliens were just right for the episode," he expressed. "Because whatever anybody may say, I think it's a comedy [....] And that's why I think that the over-the-top nature of those aliens and their screwy make up and their attitudes and their overblown posturing and stuff was right for the episode." (Captains' Logs Supplemental - The Unauthorized Guide to the New Trek Voyages, p. 65)