Before I make a big purchase, I go see a fortune-teller.
I usually have someone tell me my fortune before I spend a lot of money on something.
この場合、次のように言えますよ。
ーBefore I make a big purchase, I go see a fortune-teller.
「大きな買い物をする前に、占い師に見てもらう」
to make a big purchase で「大きな買い物をする」
to go see a fortune-teller で「占い師に会いに行く」
ーI usually have someone tell me my fortune before I spend a lot of money on something.
「大きな買い物をする前に、通常占ってもらう」
to have someone tell my my fortune で「誰かに占ってもらう」
to spend a lot of money on something で「何かに大金を費やす」
ご参考まで!