Should I sell my phone to buy one second handed?

So, I've had my iPhone 6 for a few years and it still works okay apart from the battery, but I can get that fixed for $30 so whatever. But then again, I could sell it online for 175 and buy an iPhone 6s for that same price. But second handed. The thing is, I'm not sure if I should. I really want a new phone but what if I buy one and there's something wrong with it? Should I just take the risk or stick with my old one?

Rear camera from iPhone X isn't working. How do I fix it?

The rear camera on my iPhone X stops working occasionally.

It stopped working last week, but it came back about days later. It then stopped working again two days after that. It's only the rear camera. The front facing one works, but when I try to switch to the rear camera, it doesn't work.

The camera doesn't work in any camera apps. The camera app, snapchat and instagram don't work. I've tried turning off the phone and closing all applications but it still doesn't work.

I'm on the latest firmware (11.4) so it isn't the firmware.

If anybody knows what I could do to fix it, I would really appreciate it.

Accessing iphone via text app?

I can access a text message/calling app installed on my iphone x. It has gone missing. Is there anyway for me to somehow get into the iphone from my pc thru that text app that is installed on phone?