Why do some bullion sellers not take debit card payments?

It's possible they're using the term "debit card" to refer to the EFTPOS network. EFTPOS gives you the SAV and CHQ options to pull money straight out of a bank account.

Visa or Mastercard can pull money out of a bank account too, but they do it via the credit (CR) function. If it's a credit card, the funds are drawn from a credit facility you've negotiated with the card issuer. If it's a debit card, it uses the same logic but the credit facility only extends as far as the balance you have in your bank account.

In that respect, your Visa/MC branded debit card is functionally the same as a credit card.

 

I am yet to see a online site that accepts debit card for any one off purchase. Very different to signing up for Direct Debit authority?
If we are talking about Eftpos, can a vendor even key in the numbers manually and you are going to give them the pin?

Also Eftpos have very different consumer and merchant protection

 

This is because Hotels use CC facilitate hold X dollars