Sargasso of Space

"The Sargasso of Space" is also the title of a 1931 sf novelette by Edmond Hamilton

Sargasso of Space is a science fiction novel by author Andrew North (pseudonym of Alice Mary Norton, also known as Andre Norton). It was published in 1955 by Gnome Press in an edition of 4,000 copies.
Plot introduction
The novel starts with Dane Thorson getting assigned to work as a Cargo master apprentice on a Free Trader ship named Solar Queen. A Free Trader (not working for any intergalactic trading companies) means that the crew has to take on trading contracts with remote and recently discovered planets, which can be very dangerous and unpredictable.
The crew wages all their saving, including their own salaries, to win a bid for trading right with the planet Limbo. Upon their arrival, they learn that intelligent life on Limbo is very limited and trading is almost impossible, and they also discover that they are not the only humans...