How are you proposing collecting any debts from a spammer in
BTW, to be able collect such charges you _must_ be able to prove
that the spammer have seen the price list. That is kind of hard
to do when you don't have spammer's return address. Implied contracts
have been commonly found non-binding by the courts (a typical example
would be to open a cafe, wait when people walk in and then tell them
"our admission fee is $100 -- please pay up, or we call police").