Using Best Offer you can specify two value. 

  1. Minimum Offer Price, in percent
  2. Auto Accept Offer Price, in percent

  • Your ebay product price is 100$. The minimum price for that you ready to sell a product is 80$. Price for which you are ready to sell product immediately is 95$ and higher.
  • As result, you specify in selling product
  • Minimum Offer Price - 80% 
  • Auto Accept Offer Price - 95%

If potential buyer set best offer price as 79$ its offer will be a decline (100*80/100 = 80$ minimum price).
If buyer set price as 85$ (more that minimum offer and less that auto accepts offer price) you will need to make decision accept of decline offer.
If buyer set price as 96$ (more that 100*95/100= 95) offer will be automatically accepted.