This is quite common and pretty harmless. The scratches you see don't go very deep, nor are they very wide. My All-Clad saute pan is nearing 10 years old and has a ton of micro-scratches on the interior. It still performs beautifully.
That said, the scratches can grab onto proteins and cause sticking. However, this is simple to prevent with both oil and proper pan preheating.
When a pan is preheated properly the metal expands, essentially closing all of the micro-scratches. This prevents the proteins from grabbing onto them and getting stuck. You obviously need oil/fat to assist with this as well.
To properly heat a pan to the appropriate temperature I suggest using the water drop method. If you put a cold pan on heat and drip a drop of water onto it, the water will sit there for several seconds then boil away. As the pan gets warmer this will happen more quickly, fizzling away in a second or so. Once the scratches start to close something weird happens.
First, the drop of water will break into a few mini drops which scoot around the pan as they evaporate. This is a sign that you are almost there. When the drop of water stays whole (mostly) and scoots around the pan like a mercury ball, this is the perfect temperature. I the water instantly vaporizes on contact, you've gone way too far and need to let the pan cool down. At this point you should add your oil/fat, swirl it around, and immediately add your food. (Make sure the mercury ball of water is gone before adding oil).
Also note that the mercury-ball phase is definitely too hot for unclarified butter, and may be too hot for some extra-virgin olive oils. They may instantly smoke upon adding.
Again, it's important to have your oil and ingredients in place (mise en place) before you start. It's quite easy to skyrocket past the mercury-ball phase if you have to open your oil, pour, and then season your ingredients.
Yes, you don't have the edge of a pan in the way when going to flip things, but it also means that you don't have a mass of metal there to add as a heat sink, which can help dramatically when pre-heating your pans, as they'll be evenly heated across their bottom more quickly (at least, compared to something of the same material, such as a cast iron skillet)
More importantly, in my opinion, is that without the sides, you don't hold in moist air, so when cooking things like hash browns, you can get a better crust on 'em without steaming them.
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If we are talking about the cook surface then my money tends to go towards a used one, as long as it has been properly cleaned over time and taken care of ( i.e. few scratches, dings or buildup). That being said a used one that has been taken care of will also work better for cooking because of the oils that are already seasoned into it. The thing to watch for in buying used would be the underneath, make sure the lines are good and that the underneath is well maintained. Buying used will not only save you some money but also some time and frustration from dealing with "sticking" issues which can come from using a new flat-top. Plus "used" adds character, but that's just my opinion.