I think that is a good idea. A lot of times, people will just continuously post CL ads and ask "should I buy this?", which is not really helpful for anyone. If we see something that is a good deal and tell you that it is worth it without knowing how it will fit you, that could very well be a sunken cost. There are indicators that will tell you the worth/quality of a bike such as tubing stickers, braze ons, lugs, forged dropouts, and most indicative of all are components. Most of the time, knowing the hierarchy of components can easily tell you the quality of the bike.
PS don't let anyone tell you that modern bikes are better than classic/vintage bikes. See for yourself!