c) "It depends. Some campaigns are successful in attracting / persuading / winning customers, but that's not necessarily true."
c) winning (you attract or persuade customers)
a) "Not really. I like to think that people make / take / get their decisions by themselves."
a) get (make a decision and take a decision are correct)
b) "Absolutely. The thing is: some strategies are really effective, but others are needy / poor / bad."
b) needy (you can say that some strategies are bad or poor)
e) "I'm not sure... Sometimes an ad gives me a positive / warm / hot feeling, but does that mean that I'll actually buy the product? I don't think so..."
e) hot (in this context, you can only use warm and positive to describe the feeling)
d) "100%. People simply wouldn't shop / buy / purchase certain products without the influence of advertising."
d) shop (you buy or purchase products; you can shop for products)