I am really nervous about trading in my phone to get monthly credits for a new iPhone. Does this go smoothly for anyone?

I have read too many posts here about people having issues sending in trade-ins, or them never getting received, etc. that it makes me really nervous to send one in and be at the mercy of Xfinity whether they receive it or not.  Is it possible to just return a trade in to the store and have them issue the monthly credit right there so you don't have to worry about them not receiving it?