First time buying an IPhone

Thank you in advance for answering my question. I want to buy an IPhone and it will be my first time. How can I buy an IPhone? What is the process for buying one? Also, I wanted to do monthly installments, but I'm currently building up my credit.

Will I win this case on eBay if the buyer opens one on me?

So I sold an iPhone 5s that I bought for my brother because his phone broke but after a couple of days i purchased the phone, he ordered another phone for free through the carrier insurance. So I decided to sell the phone on eBay and it did not come with a SIM card so I did not know if it could be activated or not. So I listed in the eBay description esn unknown, doesn't have sim card no returns and the buyer got a SIM card and found that it could not be activated. I told them that I had not known the status of the phone activation and that it was listed as is no returns. The sale ended a month ago and they decided to leave negative feedback stating that I sold them a phone that could not be used even though the phone turned on and was fully functional except as stated the activation was unknown. Now my papal balance is negative for the price that they paid.

I also have no idea if my paypal balance is negative because if they opened a case or not.

Why is my phone not charging?

My iphone is not charging when plugged in to my pc or plug socket, yet it still brings up my photos and music when plugged into my computer automatically, which it only does when it is connected to my phone. My phone is a 5s btw.

I forgot my apple id and the email

I updated my iphone 5s and it requires an apple id and password to actually start using the phone. The problem is that i forgot the username apple id and i forgot the email i used to back it up. I know the password though. How can i retrieve my id and log in?

How can i open my iphone 6s?

My iphone is missing a home button as in it broke off awhile back and well i factory reseted the phone because i was going to sell it to a friend and now i can pen the iphone because it says "press home to open" what do i do?

WOULD YOU RATHER - EXPERIMENT! 100 PUSH-UPS VS NONE?

My friend and I have been working on our third experiment focusing on the punishment people would endure to simply receive branded products, and we were wondering what would you rather do?!
Please PROVIDE REALISTIC ANSWERS

No. 1: Would you rather get Nike shoes only if you exerted yourself to 100 push-ups, or would you rather get the same quality shoes (unbranded, and same looks) for free, and walk away on the spot. If you do not succeed the push-ups, you either can walk away empty handed or retry.

No. 2: Would you rather get a $90 Ralph shirt for 100 push-ups or get the same quality (and looks) shirt for free. Same rules apply ^

No. 3: Would you rather get an iPhone 7 (normal sized) and run an 80km marathon, with no relief; (if you run the marathon and fail, you either start again or you don't get the phone). OR would you rather a Chinese, no-branded phone with the same power and value.

No. 4: Would you rather crack your phone and receive the latest iPhone for free, or keep your phone and receive a new one with just as much power as the lastest iPhone BUT it's unbranded.

No. 5: Would you shock yourself by touching an electric fence (with the chance of hurting yourself) and receive a big pack of Cadbury's Favourites or would you simply take home brand chocolates

No. 6: Would you do 100 push-ups to receive an expensive packet of branded chocolate (up to your choosing) or would you rather get chocolate for free, just it's homebrand.

Once again thanks guys!

Should I update my iPhone 6 to iOS10?

I have ios 9.3.2 and it works great. But everyone is like "omg u still haven't updated it to the 10? I'm afraid I won't like it? What is my phone becomes slow?