So far as I can tell from what I am reading here, you have a twx invoice, already marked as paid, for the 900 at $850 plus balance for the smart grinder. Seems like they should honour that. If they can't supply the grinder, you could wait, or claim reasonable compensation, or a refund. If they have already said they can supply the BDB, take it at the agreed price. If they require more money, get a written request. Good chance you can get it back with persistence. As for asking for a copy of a receipt, that is pretty normal, but done BEFORE agreeing to price match. Once you got a tax invoice, you have a contract.
