If your gifts push you over the allowance, the right move is simple: use the red channel and declare. You'll pay duty on the amount above the limit, in most countries only on the excess rather than the whole lot, though a few calculate it on the full value once you exceed the threshold. Payment is usually possible by card at the customs counter.
Valuation is based on the actual purchase price, which is why keeping receipts matters. Without receipts, officers estimate market value themselves, and their estimate is rarely in your favor. Gifts you received, where you have no receipt, are valued the same way, at what the item would reasonably cost.
Confiscation isn't the normal outcome for declared goods; you pay and move on. Seizure and fines are what happen when you don't declare and get caught. So the risk calculation is easy: duty on a declared item is a known, modest cost, while an undeclared one can cost you the item plus a penalty.