The first question you should always ask yourself when someone says something is "free" is "how much will this cost me"?
A company that offers "free P&P" has already bundled the cost into their profit margin, so any item will probably cost the same as one with P&P being extra.
"Free" just means you're paying for it somewhere else in the transaction.
(NB Of course this *doesn't* apply to companies who offer Free Leather Wrist Cuffs!

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