One of my tires won’t keep inflated and constantly leak air. Can I fix it or order a replacement wheel?

Sadly they are a plastic Hub. You will have to go on line and find another brand of tire from someone else to upgrade. We had one show up broken in the box that nobody caught for 6mo after the box showed up. We ordered several units and you would know that the one back up unit was the broken one. They are NOT CHEAP Either. Amazon had some and so did E-Bay.

There are several mentions of it being hard to push and steer. Have any improvements been made to address these issues? Thank you.

We purchased ours last season (winter 2021-22), so I don't know if the model shipping currently is any different. I have used ours multiple times and have had no issues pushing or steering it. When filled with 100 lbs. of deicer it will be harder to push than when empty, but has not been an issue for us. We learned from our previous spreader, do clean the spreader after each use and keep everything lubricated - it's possible that the comments about being hard to push and steer are related to corrosion and dry bearings due to lack of maintenance. Salt will cause problems very quickly if not cleaned off after each use.

Is this product good for sandspreading

Yes' mine spreads sand/salt/seed/bug killer and fert. Does everything fine for me. IDK why some people cant use this spreader right, its so easy to operate. We have three spreaders and use this one a lot, my only issue is its tires being cheap & hard. Sorry' I don't recall proper pressure here but' as an example: Many people don't understand tire pressure ratings so they just max their tire pressures out. I assume thats mostly causing the issue stated here? Never inflate a tire to the max sidewall reading on anything. Its like people see 20lbs air pressure on a tire sidewall so they put that much or even more air in it but that number is actually that tires "maximum" air pressure. One should drop its tires down by 3-5 pounds so the traction is better and their wheels won't lock up on these. I work on mowers quite often and it floors me to see people put 35lbs in their 12lb mower tires & when I ask why? "Well' thats how much my vehicle tires use, a tire is just a tire right?" Yep, see it all the time. Most don't know how so much air got into their mower tires. Like somebody snuck it in them over night..lol Anyway' the more air, the harder a tire is so the less traction you'll get from it, especially on ice/snow so if salting the pavement drop your air by a few & these units do great! Grease their gears occasionally helps out too and will makes it last much longer too.

Can this be used for fertilizer?

If the fertilizer is dry, no problem. If the fertilizer has any bit of moisture to it, forget it. Wet or moist product gets stuck in the tube it's supposed to flow through and everything gets stuck. I'm really not a fan of this purchase.