3. Any person willfully concealing unpurchased merchandise of any mercantile establishment, either on the premises or outside the premises of such establishment,
shall be presumed to have so concealed such merchandise with the intention of committing a wrongful taking of such merchandise within the meaning of subsection 1, and the finding of such unpurchased merchandise concealed upon the person or among the belongings of such person shall be evidence of reasonable grounds and probable cause for the detention in a reasonable manner and for a reasonable length of time, of such person by a merchant, his agent or employee, in order that recovery of such merchandise may be effected, and any such reasonable detention shall not be deemed to be unlawful, nor render such merchant, his agent or employee criminally or civilly liable.