How do I make a recommendation easy for someone to decline?
A useful recommendation leaves room to say no. Start from what the person has told you they like and what's going on for them right now, and offer the suggestion as an option with enough information to judge it. Don't book, pay or invite anyone just because the option looks like a fit.
Tyra Banks described using a planning assistant to find activities she followed through on. Her preferences are hers. The bigger design question is how a recommendation lets the person on the other end choose.
Make declining easy, and make correcting easy too. If someone passes, ask whether the trouble was timing, location, cost or the activity itself. One refusal isn't a permanent preference.
Seeing an idea and committing to it are separate steps
Someone can enjoy seeing a suggestion without wanting a reminder, a calendar entry or a steady stream of similar ones.
Over time, look at what proved useful through explicit feedback and through follow-through you're permitted to observe. The point is less planning work with the person's choices intact. A recommendation that adds another obligation to manage misses that, even when the activity itself is appealing.
What to try this week
Pick one suggestion your tool makes and check what it takes to decline it. If declining takes more effort than accepting, fix that first.