It would be pretty easy for someone to collect a serial number, report it as stolen and if it pops up again just go to the police and they will take it from the owner. I owned a bass for a year not knowing it was stolen in the past. The police showed up with a police report and took the bass. They didnt even care to follow up with whom i bought it from and despite calling them 3 times and going to the police station twice they basically just told me they dont care. So the "owner" got his bass back, the seller got my money and I am out $700. Fun stuff. I can totally understand blurring serial numbers. I dont do it but anytime I buy a used bass on ebay or craigslist I print out screen shots of the ads, the seller info ( especially phone numbers), screen shots of texts with there address etc. While not necessary to blur serial numbers it does have a reasoning. Personally beyond showing the first few digits that state the year I dont know why anyone needs to know the rest, or at least be publically shown it.