Beg to differ. Substance is one element of a common law contract. Substance doesn't mean the entire amount must be paid in specie. It means that a token or symbolic amount of $1 or 1 pound sterling represents the substance. The remainder of the exchange might take place in chicken manure or brass farthings. This remainder is called "other valuable considerations". An autograph (being private property) might be considered to be satisfactory to fulfill this remainder. If dealing with family members (or pedophiles for that matter) the "other valuable consideration" might be termed "love and affection". Clueless is how I would classify those who would insist upon an entire transaction being performed in specie. First, it ain't going to happen. Second, if it did happen, you would likely hoard it and insist that you were as poor as the other 99.9% of the population that holds money as the master of their soul.