You're a private seller with a no returns policy, so don't have to accept a change of mind return. If you do, the buyer pays the return postage cost and will receive a full refund of their original payment. You can't offer a partial refund on the return of the printer, only if they keep the printer, if this is done via an eBay return.
This also only works if they open an eBay return and select 'change of mind'. If they select "Doesn't match description or photo' then you'll pay for the return.
In your shoes, I'd tell the buyer to open a return and select 'change of mind'. They'll then have to send it back themselves and you can try issuing a partial refund when you get it back. I've no idea if the system would let you, I can't see why it shouldn't. You'll need to make the partial refund via the refund section, not the return.