They need to be able to say no. According to Recital 42, "Consent should not be regarded as freely given if the data subject has no genuine or free choice or is unable to refuse or withdraw consent without detriment."
Imfuneko: "'Timvume yesigqoko ayinikezwa ngokukhululekile uma isihloko sedatha singenakho ukukhetha kwangempela nokhululekile noma ayikwazi ukuhoxisa noma yenqabe imvume ngaphandle kokulimaza. "