Pick a room. Guess which ordinary things are worth money. Then see what sellers ask on eBay, live. Free, no app, no sign-up.
How we decide. We look up what sellers are asking on eBay right now for that kind of object. GOLD means half of the listings ask $50 or more; IT DEPENDS means $20 to $50, or a quarter of them ask $50 or more; OLD means less. These are asking prices, not sold prices and not an appraisal: condition, maker and model decide the real value. For anything valuable, ask a certified appraiser.