As much as I personally dislike it - paypal is your best friend.

It allows the hassle free transfer of funds, internationally, with minimal exchange of information (just an email address in most cases).

Do not worry if you - personally - do not have a paypal account.
Do what I used to do. Find someone else with an account and give them the cash to pay for it for you.

Likewise if you are selling goods the money can be transferred to a friend or relatives paypal account and you can get the money from them.

If you are buying or selling within the same country then a cheque sent by post will usually work quite succesfully.

Bear in mind that cheques almost always are of no use in international sales.
Even if both parties have an account with the same bank: ie: hsbc.
The bank will still not accept a cheque drawn on an account from a branch in another country.
(believe me I've tried just about everything over the years.)

One other option you might consider are pre-paid cash cards. Where the money can be withdrawn from pretty much any cash machine worldwide.
Just make sure that the card and pin are never sent in the same envelope.
The sensible option would be to post the card and email the pin number.

For the vast majority paypal will prove to be the simplest and easiest method.

It is strongly recommended NOT to send cash via post. As there is no reliable way of proving whether or not it arrived, and this can lead to friction between the parties involved.

If anyone has any other methods of exchanging funds for goods please feel free to add to this thread.
CA