You can make them stack in almost all conditions. Takes some practice, but they really aren't that complicated. I started running our pull type (1037) at the age of 15, and after the first day, started getting along pretty well. You will learn some the hard way, as in your stack will fall over, and you'll be out there hand stacking it, but you won't make the same mistake again. There are tons of adjustments, and sometimes you'll have to change them from field to field, or depending on what baler baled the hay. Lots and lots of practice will help. I stacked close to 100,000 bales one summer with that 1037. Now, for the weak points.
These are the spots most likely to have broke, and been fixed, so look for welds. The load arm. It hangs out there, and every time you hit a bale, and beats on it a little. If you set it too high, then it stresses it loading the bale, set it too low, and it digs into the ground They often are broken. Secondly, and mainly only a problem on pull types, is the rolling rack. Just not strong enough, plus trying to unload partial loads, and they often will be broken off, and re-welded. Check the frame, I know ours had been broken. Also check the rims real close, we had several crack, and break the centers out. Not a huge deal, just gotta buy a new rim. Other than that, just look at the chain wear, and hydraulic leaks, (hoses, valves, cylinders, motors, etc...) but that can all be repaired if need be. Finally, check all the pins on the tables. Just my observations.