How do you go about selling large speakers?

These are too big to ship any other way than on a pallet. Pricey, especially if you need a liftgate. On the positive side, insurance is cheap but how much are these really worth? I doubt you'lll find a buyer willing to pay freight.

So, local sale is your best hope...

As others have said, post on Craigslist or US Audio Mart. They're both free and can be relisted for free withotu limit.

Don't bother with Ebay, too high a risk of an "unsatisfied" customer to screw you.

Nothing is too big to ship. Larger items need to be packed more carefully and may require a pallet as art_boston replied, but that extra trouble may be mitigated if you can ship via freight carriers (trucking firms) and not the common package carriers. UPS or FedEx do freight as well but tend to be more expensive unless you ship regularly and can negotiate a better than over the counter price - up to 75% less.

Insurance can be a problem as some freight carriers want to pay by the pound but many will allow you to set a value on your goods. Also, you can save a lot by taking your gear to the trucking depot and asking your buyer to pick up at the same. Most freight companies don’t do door-to-door well and charge a lot for "last mile" service. That is often true for UPS and FedEx as well.

When I buy and sell gear I always take and pickup my gear to the local UPS or freight depot. It’s less expensive and I suffer much less damage or breakage than by door to door. It’s on and off the little truck where most damage occurs. Skeptical? Ask someone who works at UPS. They will tell you the same thing.

I have bought and sold audio equipment on LETGO....

I just sold my Lascalas with the additional reflex bin on craigslist.

Local pickup on Craigslist