In case anyone's interested, it was asked further up this topic .. the correct syntax to check for more than one payment type at the same time is as follows. At least it worked for me:
Code:
{if $order.payment_method eq "Money Order" || $order.payment_method eq "Cheque/Check" || $order.payment_method eq "Credit Card - By Mail"}
Our address:
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{$config.Company.company_name}
{$config.Company.location_address}
{$config.Company.location_city}
{$config.Company.location_state}
{$config.Company.location_zipcode}
{$config.Company.location_country}
{/if}