back up vs shop at

back up and shop at both are verbs.

Word	Noun	Adjective	Verb	Adverb
back up	No	No	Yes	No
shop at	No	No	Yes	No

As verbs, shop at is a hyponym of back up; that is, shop at is a word with a more specific, narrower meaning than back up:

back up (verb)	shop at (verb)
establish as valid or genuine	do one's shopping at; do business with; be a customer or client of
become or cause to become obstructed
make a copy of (a computer file) especially for storage in another place as a security copy
move backwards from a certain position
give moral or psychological support, aid, or courage to