In a recent Fundraising Magazine (from Civil Society and included with your CIoF membership) an article argued that charities should be more prepared to say no to donations.
Now as a volunteer fundraiser myself, that initially makes little sense, but of course there are occasions when declining a donation is the right thing to do.
The article specifically raises the issue of donor dominance, where a donor (individual, trust or corporate) acts in ways that are not acceptable. Another scenario is where it can be unhealthy for a charity to become too reliant on one donor.
Every organisation should have a policy on the acceptance and refusal of donations, and codes of conduct that apply to staff, volunteers and donors. On the former point, the CIoF has a very helpful free resource that you can download from https://ciof.org.uk/events-and-training/resources/acceptance,-refusal-and-return-a-practical-guide-t and this also discusses the difficult issue of returning donations (including when to involve the Charity Commission).
I hope that you ensure that your organisation, and your fundraisers, are given the protection and support they need.
As I am currently working on a review of this area for a number of charities, if you would like to have an initial chat through the issues, you can contact us in the normal ways, use the contact form at https://zorva.info/about-us/contact-us/ or book a free 20-minute insight call at https://zorva.info/free-insight-call/