It depends on the contingency. If the sale is contingent upon the buyer obtaining financing and they appear to be qualified that might be acceptable.

However, if the contingency is that the buyer must first sell their home before they buy yours I would strongly recommend against it unless it’s already in escrow. There’s no guarantee that their home will sell or much less close. Now you’ve taken your home off the market and could miss the opportunity to sell to another qualified buyer with no such contingency.

Let them at least get their home into contract before considering a contingent offer. In the meantime, market the heck out of your property.