UPS has a pack and ship service. You or the buyer can make the arrangements, I would simply do this:
1. find the closest UPS that does pack and ship (they all do not).
2. give the seller the UPS contact info, the weight and measurements.
3. let seller make his own arrangements, you simply drop them off unpackaged.
IF you have factory packaging, tell buyer you will give it to UPS separately to use or not, his/ups’s choice, after they are dropped off.
I’ve used UPS Pack and Ship successfully 3 times. We can use it to buy something seller says is local pickup only, all seller has to do is agree to drop them off for us.
btw, this keeps the shipping cost out of any system like eBay that both charges tax on shipping, and charges a fee on the shipping and tax amounts.