Yes, I've bought lots of "Refurbished" things. In the US, once it comes out of the box, it's used and cannot legally be sold as "New", so since it's technically not a "Used" item, they are supposed to check it out, fix it and call it refurbished. That means, the problem could be anything from the buyer had "Buyers Remorse" and there was nothing wrong with the gun, to, the gun was a complete lemon and the buyer sent it back for replacement. If the vendor did their job and fixed all the issues, that is great, but sometimes the issues are so small, the vendor just resells a substandard product.
Example, I bought a Nikon camera with a 300mm Zoom lens a few years back. The zoom ring was so tight (probably why it got sent back in the first place) that you could hardly turn it. It worked, but definitely wasn't what I expected from Nikon. I kept it and it loosened up over time, but was technically still defective when I received it. It's been a great lens, but still a bit stiff. You run the same risk with air rifles.
To be honest, I wouldn't hesitate to buy a refurb from a reputable dealer that'll take it back if it's really fouled up. They are just trying to salvage what value they can out of the gun without throwing it in the dumpster, which does happen.
Do be careful and make sure it's a reputable dealer - It'll pay off in the end.