Shouldn't "scale" be accepted too?
In place of "weigh"? "scale" is possible in that context but is very unusual. People will think you are an ant climbing over the apples.
The English noun "scale" = "scara" in Romanian. Can "scara" be a verb? (Please forgive my lack of diacritics.)
why we cannot say "Please, you weigh these apples"
"Vă rog" strongly suggests that the following "cântăriți" is an imperative. Context matters.