Reading a series where book one is clearly weaker than later volumes

Someone keeps recommending a fantasy series to me with the warning that ‘it gets amazing around book three.’ I can believe that an author improves, but two full novels are a fairly big entrance fee. I have stuck with mediocre first installments before and been rewarded; I've also resented every hour. When you recommend a series with a shaky opening, do you honestly tell people to skip the first book, or is the later payoff too dependent on the setup?