Being straightforward when turning down requests doesn’t mean you’re being discourteous. In fact, your candidness is likely to be appreciated by the requestor, who’ll know that trying to persuade your accommodation will be a waste of time. The individual can spend that time more wisely looking elsewhere for assistance.
Consider the following two responses to a request for help…
“I don’t have time to help you.”
“I don’t have time to help you because I’m working on a crucial report that’s due in two hours.”
The first response prompts the requestor to wonder whether your refusal to help is a personal rejection. That can lead to a confrontation, which helps neither party.
The second response eliminates rejection as a possibility. Instead, it justifies your decision as reasoned and practical. The requestor may dislike your decision, but will be more likely to accept it at face value.