it seems to me from your previous questions that you do not live in the United States; so my advice is generic about treadmill selection without any specific advice.
Make sure you check the weight limit of the treadmill. Some treadmills have recommendations that the user may not weigh more than 250 lbs. (about 115 kg). While they are usually usable beyond that limit, a warranty may not be honored. Consider how the treadmill will be used. If it will be used commercially and runs all the time, you need to go to the high end of the market. But if it is for home use for a 30 minute walk 5 times a week, a very basic model will often suffice.
If it is for home use, you usually have a choice between one that folds up for space preservation and for one that does not. I found that the ‘space savers’, once folded up, never see the light of day again (personal opinion). They also may have different length and width of the band; that is a matter of comfort and personal choice. If you want to run, though, I recommend a longer band.
Most treadmills now come with the ability to measure heart rate through transmission from a heart rate monitor or by sensors built into the handles.And finally: all treadmills have pre-set programs. If you really enjoy those, pick one with a lot of them. But many people use the manual option only and end up having paid a lot for things they don’t use.
I hope that will give you some ideas of what to consider when purchasing a treadmill.