Turning down a project
Quick and clear. A slow no wastes their time as well as yours.
Subject: Re: [project]
Hi [Name], Thanks for thinking of me for [project]. I'm going to pass on this one — [short honest reason: capacity, fit, timing]. [Name] does excellent work in this area and might have room: [contact]. Happy to make the introduction. Do keep me in mind for [what you do want]. [Your name]