Transparency helps everyone!
It is good practice to tell potential other buyers that you have conditionally sold when they schedule a viewing - this way they have the information upfront.
It is definitely important to tell any new potential buyer if your home is conditionally sold before they make an offer.
If you DO accept a second (or third) offer, be sure to include this statement as a seller's condition: “The acceptance of this offer is subject to the collapse of the original offer that is already accepted.”
Even at this stage of your journey, our Seller's Checklist has tips from negotiation and beyond!