50% off what? A better way to judge a deal
Compare the exact product and the final checkout cost before treating a discount as value.
The useful answer
A percentage discount does not establish value by itself. Match the exact model, size, condition and seller, then compare the final cost with reliable observations for that same product. A reference price is not a price history.
Match the thing you will receive
A different capacity, color, regional version or used condition can make a comparison misleading. For a keyboard, layout matters; for skincare, package size and formula matter; for a charger, port count and supported protocols matter. Check those details before comparing a headline saving.
Separate reference price from observation
A reference price is a comparison anchor. An observed price is a recorded offer at a stated time. A historical low requires an actual observation history over a defined window. These should not share a label. If a history is missing, say it is missing.
Make the total useful
Shipping, tax, subscriptions, membership and required accessories can change the real cost. A small speaker without a charger may still fit your setup if you already own the right charger; it may cost more if you do not. Compare the purchase you need to make, not just the box price.
Use a need-first test
Would the product solve an existing problem without the discount? Does it fit your budget and existing equipment? Is the return policy acceptable? Skipping an unnecessary purchase can save more than choosing the largest percentage off.