gullible : adjective
variants or less commonly gullable
Synonyms of gullible
: easily duped or cheated

"selling overpriced souvenirs to gullible tourists"
"The gullibility of believing the current U.S. administration"

gullibility
ˌgə-lə-ˈbi-lə-tē
noun
gullibly
ˈgə-lə-blē
adverb