Buy defective smartphones (what's worth it)?

Since I have dealt with PC & smartphone repairs a lot over the years and have now acquired some knowledge (screen, swapping experts, programming, setting up, etc.), I thought about buying, repairing and selling defective smartphones / Laptops and PCs something to earn.

Now I would like to know your assessments, maybe we have a few experts here.

There are smartphones that have a damaged display and where it is still worth repairing.

But now there are also displays where, for example, it says: device no longer starts, water damage, etc.

Is it even worth buying these devices? Of course, most of the time these are relatively cheap and you wouldn't make a big loss.

But can water damage be repaired in such a way that it is still worth it or if the device e.g. No longer works and you have to assume that there's a short circuit, etc., is it still worth it? And if so, what kind of approach do you use?

E.g. A laptop that simply doesn't work anymore is ultimately not repairable or only involves a lot of effort / expense.

I mean, of course, you can then swap the mainboard, for example, but that's actually no longer worth it, is it?

I would rather buy smartphones with a damaged display and then get the new and original display on Ebay or anywhere else. When changing, you can't break a lot either way.

Water damage is gross
everything corroded. There may have been a few short circuits and components on the board itself have been destroyed.

It is worth repairing Nintendo Switches, they usually only have small defects, which is why they don't work.

Yes you are right.

Water damage can completely destroy all components and the only thing that helps is replacement.

What about devices that no longer work, for example, and have no water damage? Is it worth trying to repair something like this or is such a short circuit irreparable or is it more likely that it is due to something else and the purchase is worthwhile?

When you can't see what it is from the outside. Very risky.

Could be a dead board. Broken switch. Loose cable.

Most broken cell phones don't just break, people drop them. So much can happen there.

If you want to earn a little something, stick to the cases where the damage is clear (but there can also be something on the board)

Okay thanks.

Are there such "favored" devices where you can make a good profit without investing too much? As I said, it should only be a side income but don't want to buy any old devices with which you don't earn anything in sales.

I now have a Huawei Y3 from 2019 with display damage, the display costs 12 euro.

Are there any tips or things that are particularly good for a start until you have a small income?

Someone wrote, Nintendo Switch, however, even defective, they are still traded at 200 euro upwards ^^

What is currently offered and is still relatively new.

Almost no one will buy an old cell phone and use it and repair it.

Switch is great, yes
But they are also super repairable and people know that too.
But if you get an unpatched one, there are people who will lay down even more for it, because you can very easily use custom firmware there.

I'm one of the lucky ones and have a switch from the start and therefore unpatched.
I'm sure not to give it away! Homebrew for Life!

Okay, first of all thank you for the time, you will definitely get the most helpful answer.

Are there tutorials or books or something for further education? I taught myself to have fun but never managed to do it professionally.

If you have any other tips, please let us know.