Totally agreed. I did try once in fixing my door. The tuning of the spring is not simple. You will need two long bars to wind the coil spring. Not a simple task if you are not handy enough.
Don't do it yourself! You probably don't have the right tools.
My garage has that changed five months, and was told those springs can be used for 10,000 times (opening).
The professional spent around 1.5 hours to change both,
Your Garage roller bearings probably failed to work also...
I live in Toronto, and the guy came late at night (11:00 p.m.), he changed both springs, and I paid 200 CAD (not bad, since that was 1.5 hours labour, and parts (two springs), and since I bought those rollers and changed them free for me).
The spring used by LZ is never avaliable in HD. It is only avaliable to a licensed contractor. Yes you need a licensed to install garage door in Ontario. Usually you need professional to install it. I think it is around 200 dollars. You may save 100 dollars if you only order the spring from the contractor and DIY. I let a contractor fixed mine fews years back. He did in 15 MIN. I think I should be able to do it myself next time after I saw what he did. The key is don't use two bar to tension it, use one bar and one vise grip. You tension it with one bar first, put vise grip on the axle hold is postion so it would turn back. tension another turn with the bar.... You have to stand face parallel to the axle , turning bar in front of you.
But after all its trouble.. I would just pay the guy.