Welcome to SRP. I usually recommend a new razor to those starting out because it is a known quantity. For the most part the razors offered in the SRP classifieds will be high quality and if the seller says they are shave ready they ought to be. If you go the antique store route IME the sellers there often have an inflated view of what their wares are worth.

If you go to the "razor clubs" forum here you'll see some of the razors members hold in high regard. In most cases only good condition razors are posted in those forums with full blades, little or no hone wear, chips or cracks on the blades. Scales (handles) should be in good shape, preferably original if it is a collectible, with no cracks or the dreaded cell rot. That is what you want to look out for if you go razor hunting.