Lawnmower cutting uneven

A bent spindle will give you a bad cut, but so will improper tire pressure, a twisted or broken deck, worn deck suspension components, and other similar conditions, depending on your particular mower. So, I would start with the basics. First thing first, do you have the owner's manual for your mower? If not, you can probably get it online, or from your lcoal dealer. The manual may very well provide you with more detail regarding some of the things that I or others will mention. Meanwhile, I would park the mower on a level concrete surface, inflate the tires to the prescribed pressure, and begin with a thorough visual inspection, primarily to determine if the deck hangs level from the drive unit, etc.; look for any worn or craked components that suspend the deck, and use a tape measure where applicable to compare side to side variances. Next, I would want to see if the blades appear to cut level. So, block the mower such that it cannot roll forward or back, and disconnect the cable from the negative battery terminal, to prevent the engine from accidently firing. Now, measure the height of each of the cutting edges of the blades from the floor. Also, pick a spot on the deck for each blade, from which to measure how close the blades comes to the deck. It will be hard to get a tape measure or ruler in there, so a socket, scrap of wood, or other fixed length object will work, as you are not concerned with the actual measurement, but how they all compare. Now rotate the blades 90 degrees, and repeat the process, then again at 180 degrees, and finally at 270 degrees. If you have a bent spindle, it should show up as you compare your measurements. You will very likely find that the blades are lower at the back of the deck than at the front, but the sided to side comparisons should be most revealing.