These templates are a starting point for your communication. If you don't genuinely care about making your customers feel good, or don't want to treat them with empathy, no template will help you. Remember: read them, copy & paste them, and then adapt them to your own voice. You'll have much more success.
Thank you so much for your generous offer of [ Offer ], [ Name ]. I appreciate the thought & energy you put into it! That being said, this isn't a fit for me right now. If things should change down the road, I'll be sure to let you know.
That said, if you ever have an offer that's [ exactly what you want ] please feel free to send it my way -- I'd be very interested!
Thanks so much, [ Name ].
Unfortunately that won't be a fit for us. [ Explain in one broad sentence why it's not a fit: we're not taking on new clients at this time / we've already allotted our pro-bono budget for the year / our schedule is booked through XYZ date ].
Wishing you the best.
Thanks, [ Name ]. That won't be possible for us.
* Sometimes you'll encounter a very persistent person who doesn't want to take a polite "no," for an answer. Rather than getting feisty, just repeat this magic phrase over and over: "That won't be possible." Don't explain, don't apologize, don't elaborate. Just politely repeat, "That won't be possible," until they realize you won't engage.