The origin of scam, (meaning, trick, ruse, fraudulent scheme) is obscure or unknown; it might be related to British scamp, a cheater, a swindler. OED has it first cited in 1963, but it seems that there are much earlier entries.
OED does not cite different definitions for the word, such as scam meaning to hurt, shame, also meaning to stain; spot or scorch.
Looking up shame in the OED, it seems that the word is a cognate of ME scam.
Forms: α. OE scamu, sceamu, OE–ME scame, ME same, ME seame, ME scam,ssame, ME, 15 Sc. scham, ME, 15–16 Sc. schame, (ME chame), Sc. schaym(e, ME, 15 sham, 15 Sc. schamme, scheyme, ( schaheme), ME– shame. β. OE scomu, scomo,sceomu, ME scome, ME sceome, some, ME scheome, schom, ME schome,shome.(Show Less)
Frequency (in current use): http://www.oed.com/frequencybandinformation/6
Etymology: Common Germanic: Old English sc(e)amu, sc(e)ǫmu, corresponds to Old Frisian scome, Old Saxon skama, Middle Dutch schame (modern Dutch schaam- in compounds), Old High German scama (Middle High German, modern German scham), Old Norse skǫmm with unexplained gemination (Swedish, Danish skam), Gothic *skama(inferred from the derivative skaman (reflexive) to be ashamed) < Germanic *skamō.
From the Germanic root *skam- are also Old High German scant ashamed ( < *skamdo- ), Gothic skanda , Old High German scanda (German schande ) feminine, disgrace, Old English scand (masculine), infamous man, scand (feminine), infamous woman, disgrace, scęndan ( < *skamdjan ) SHEND v.1
There are a few entries recorded in the CHAE that predate the OED’s:
1840: ,” traitor, take thy rest! Ha!—are those scars, that scam thy aged breast?—And didst thou think’ those poor dumb wounds would…”
1892: “faker, that is, a con man who runs a fraudulent lotion and cream scam; “ George Reeder, proprietor of an intelligence office, “ who is literate…”
1958: “ also was critical of the Assistant to the President for declining to testify.’ Scam Verdict’ “ I’d say it’s a Scotch verdict: not proven,..”
Not certain if all of these are related to fraud, trick, swindle…
Another hypothesis is that it derives from the word, escamotage, which is not recorded in all dictionaries. I doubt the legitimacy.
What say you??