The former Celtic, Arsenal and Wales man was commenting after 25-year-old striker Bony was linked with several clubs thanks to his 25 goals in 2013/14.
He could star in the World Cup in Brazil after being named in the Ivory Coast squad, further upping his value, and making it even more difficult for the Swans to keep hold of him.
Bony has lifted Swans fans’ hopes by pledging his future to the club in the past week.
But Hartson is reported by BBC Sport as saying: "There's going to be bids, it's just how strong Swansea City are in terms of holding on to these guys.
"Swansea are a selling club. They like to make money and like to bring players through and sell them on.
"It's going to take a strong board and a strong manager to say 'this player is vital for next season.'.
"Bony's attitude, does he want to stay? Will he make noises if a Man City or a Bayern Munich come in?
"I would like him to stay. I want Swansea to keep all their best players."
Bony came to Swansea for a club record fee of £12m, from Vitesse Arnhem in July last year.
But he might not be the only player leaving, according to Hartson, who has questioned whether Michu will stay.
His season has been plagued by injury, but he was top-scorer for the club in 2012-2013.
Michael Laudrup, former Swansea City boss, signed him from Rayo Vallecano for £2.2m in July 2012.
"Garry Monk may well want to keep him but I read some of Huw Jenkins's comments and Huw Jenkins wants Garry to look at players that are going to go straight into the first-team.
"They want the squad to be competitive, they don't want to be carrying squad players on two or three year contracts."