Do not counter yet on the 2nd offer until you extricate yourself from the first (assuming you can extricate yourself)--otherwise, if you counter to the 2nd offer and those buyers take your counter and the first buyers fulfill their contingency, you will be contractually obligated to sell your home to two different people--which means at least one of them can sue you for breach of contract and/or fraud. You have to wait until the first buyers fail to sell their home within whatever time frame is given to them and the first deal terminates before you can safely counter, since your counter becomes an offer that the person being countered to can accept, creating a binding agreement, even if their acceptance would be bad for you under the circumstances.