That's what I always do for large amounts and at places where they accept credit cards.
「高額且つクレカ払い可能なところでは常にそうしてる」=>
"That's what I always do for large amounts and at places where they accept credit cards."
クレカ払い可能なところ = places where they accept cards; places where they accept credit cards
高額 = large amount (of money); large sum (of money)
常にそうしてる = I always do that; That's what I always do.