Import charges are only due on items with a value of the equivalent to £36 (around $70) and excluding postage or more. This is the value at which items can be gifted so generally there is no charge on anything up to that value.
Above that amount you are liable for VAT on the excess and more than likely a handling charge from your local post office. These are paid when you visit your collection office to pick up your parcel.
I generally order between $50 and $60 of stuff at a time from the US (at the shop mentioned) and have never had a problem with customs or the postman.
The bit the shops won't like is that even if you do get caught for import duty and a handling charge the items will still work out cheaper than you can buy them in the UK