I think this post illustrates the point well. Condition is subjective, especially if vague descriptions are used for the overall bike rather than detailed descriptions of the parts. To some people, "ready to ride" as a description of a used bike - and especially one of some age like many on RB - might mean that it's basically in serviceable order mechanically; to others it will mean that every gear clicks perfectly, the wheels are absolutely true and smooth, there are no parts looking in shabby condition, etc. Some people might say one worn chainring is no big deal if that's the only issue with a used bike of some age, while others will get angry about it not being what they thought they were paying for. I'm not saying one is right and the other is wrong and there's no point judging since I don't know either what was advertised or what was received, but it illustrates how different people can have different expectations which mean they interpret the same words differently.
A while back I bought a modern Klein on ebay. The condition was not brilliantly described, something like "generally very good" etc, and if it had been it would have been a good price. I'm not sure I'd have bought it without the safety net of the ebay return policy in the first place though. When it arrived although it was 'rideable' in some sense, the Death Grip tyres had perished badly, the disc brake pads were worn through, the rotors weren't true and needed replacing, the shock had an oil leak and the drivetrain was plenty worn. Any one of those issues I could really have lived with, but with them all together, overall it was just not the deal I'd expected it to be and if the listing had described those issues instead of "generally very good" or whatever it was, I certainly wouldn't have bought it at the price I paid. I didn't really have to think twice to open an ebay dispute to get a refund on it while the seller was of course disgruntled (made a comment along the lines of "it's an old used bike, what did you expect?") and probably genuinely felt like I was being unreasonable. But the customer is always right on ebay.