Old English sellan "to give, furnish, supply, lend; surrender, give up; deliver to; promise," from Proto-Germanic *saljanan "offer up, deliver" (source also of Old Norse selja "to hand over, deliver, sell;" Old Frisian sella, Old High German sellen "to give, hand over, sell;" Gothic saljan "to offer a sacrifice"), ultimately from PIE root *sel- (3) "to take, grasp."
Meaning "to give up for money" had emerged by c. 1000, but in Chaucer selle still can mean "to give." Students of Old English learn early that the word that looks like sell usually means "give." An Old English word for "to sell" was bebycgan, from bycgan "to buy."
Slang meaning "to swindle" is from 1590s. The noun phrase hard sell is recorded from 1952. To sell one's soul is from c. 1570. Sell-by date is from 1972. To sell like hot cakes is from 1839. Selling-point attested from 1959.
To sell (someone) down the river figuratively is by 1927, probably from or with recollection of slavery days, on notion of sale from the Upper South to the cotton plantations of the Deep South (attested in this literal sense since 1851).
"bookseller," 1775, from Latin bibliopola, from Greek bibliopōlēs "bookseller," from biblion "book" (see biblio-) + pōlēs "merchant, seller," from pōlein "to sell" (from PIE root *pel- (4) "to sell"). Especially a dealer in rare or curious books. French has bouquinist "a dealer in second-hand books of little value."
"a state of limited competition in which a market is shared by a few producers or sellers," 1887, from Medieval Latin oligopolium, from Greek oligos "little, small," in plural, "the few" (a word of uncertain origin) + pōlein "to sell" (from PIE root *pel- (4) "to sell."). Related: Oligopolist.