When it comes to high end electronics, rule of thumb is always document the chain of custody. If buying it from someone, buy with a C. Card which has in-built insurance so-to-speak against this kind of fraud, or paypal, which has protections. Never cash or btc.
Save every conversation and email it to yourself which will create a server timestamp, in the case of any police report issues.
Also, if buying a "new" product, take a picture of unboxing using a current-day's newspaper to established it wasn't in fact opened 6 months ago.