import tax is by the country you live in and not by the seller.
if your country didn't charge you - consider it lucky. Every country has tax laws to charge on personal imports.
if you went through proper declaration - then you are surely going to be charged.
a lot of times, the freight forwarder don't declare fully, or some times each country could have allowances, ie x amount of free per year and under certain values.
Tax is a bit more technical, there could be VAT/GST on the invoice value.
then you could have import duties, that is based on what the product is, and where it is made (country of origin)
in some cases, one would have to pay VAT and Duty, and that could some times "double" the value of the product easily.
So to cut the long story short, go and google the import tax threshold, or even ask the freight forwarder.
To assume there is no tax, because one "got away with it before", is really just being lucky.