A good offer is really subjective, based on your perception of how close it meets your expectations. Considerations include the price, terms, closing date and many other factors.
For some people, price is the most important variable, while others are more focused on the close date, or a need to stay in the house for a short period after closing.
If you have multiple offers, you can compare offers to see which one stands out from the others.
If the offers are not meeting your expectations, it does not mean they are not good of “fair” offers. If the offers are lower than you hoped for – but are in a limited price range – then the offers are probably representative of the current market value of the property and should be seriously considered.