If I have a typo on eBay and have received a best offer...?

You need to contact the buyer, whoever ends up giving the best offer, and explain the situation. You should also contact eBay's customer service and ask the best way to fix this. If someone ends up buying it, you must contact them and explain yourself, which is best done via email so that you have a written record of the conversation. I'm sure the buyer will understand and appreciate the honesty.