Why doesn't Haley want Hagar?

From the text:

"Find it a tight pull;—why, she's an old rack o' bones,—not worth her salt."

"You wouldn't then?" said the man.

"Anybody 'd be a fool 't would. She's half blind, crooked with rheumatis, and foolish to boot."

"Some buys up these yer old critturs, and ses there's a sight more wear in 'em than a body 'd think," said the man, reflectively.

"No go, 't all," said Haley; "wouldn't take her for a present,—fact,—I've seen, now."

"Wal, 't is kinder pity, now, not to buy her with her son,—her heart seems so sot on him,—s'pose they fling her in cheap."

"Them that's got money to spend that ar way, it's all well enough. I shall bid off on that ar boy for a plantation-hand;—wouldn't be bothered with her, no way, not if they'd give her to me," said Haley.