Cash on delivery works like this:

You go to post office and tell them you want to send it Cash on Delivery.

They send out the parcel.

Parcel is received on the other end and if accepted, they will pay for the package.

Once this is done, a money order is sent to you. A money order is like a postal office cheque, just as good as cash almost except the fact that you have to cash it first.

It's perfectly safe for you as a seller.

From the site:

"COD is a service for domestic mail for which an amount due to the sender, up to $1,000, is collected from the addressee before delivery and returned to the mailer. It is a service available to consumer and business mailers. COD is available for parcels only or items mailed at parcel rates.

The amount collected from the addressee can include:

Amount representing the value of the item.
Service charge in the case of repairs.
Sales tax.
Postage.
COD fee and special service fees.
COD cannot be used to collect on items not ordered or requested by the addressee or to collect money owing on previous accounts. Indemnity is available up to $1,000. Items sent COD must abide by Canada Post mail preparation requirements. The amount of the COD collected from the addressee will be forwarded to the sender by Postal Money Order when payment is made by cash or by cheque drawn up by the addressee payable to the sender. "

It's not a bad method of payment, but you will have to pay a little extra, of course you can just make them pay for it. Got a link to where/what you're selling? I'd like to see

Thanks