Muzukashii desu ne (難しいですね): that is difficult. A common way to refuse a request politely without saying no.
Maemuki ni kentō shimasu (前向きに検討します): we will consider it positively. Sometimes used to avoid an immediate answer or to decline gently. It is not a promise.
Kekkō desu (結構です): that is fine. It can mean acceptance or refusal, depending on the situation.