UPDATE 12/5/20 :
I recently came across new information while continuing my research into this topic. I have updated the Resource section at the bottom of this blog post to include an article on Cryptovantage.com by Arthur Crowson that breaks everything down perfectly. I have also included a link to his bio for anyone interested in checking him out.
It is by far the most extensive explanation of the advantages and disadvantages of using Coinbase Mobile vs. Coinbase Pro that I can find.
I don't know how I missed it when I was gathering my information the first time around, but better late than never!
The only thing I can think of is that the Google search algorithm left it off the list in favor of their sponsored articles.
I recently switched to Brave Browser along with the Duck Duck Go search engine , and I have noticed a big difference in the content that pushed to the top.
ORIGINAL ARTICLE:
Well, either I didn't read the Coinbase TOS close enough, or I have been getting ripped off and never even realized it until this morning.
While looking through my Coinbase portfolio this morning I decided to convert some of my Bitcoin into XRP because the price of XRP had dropped to $0.61per coin usd.
I don't have a lot of capital so every move, and every .01 counts. I had moved my original bag of XRP into Bitcoin early this week when prices were up , so I saw an opportunity to buy back in cheaper with some of my profits.
To keep a long story short, when I checked my transaction verification the price per coin did not match the chart I based my buying price off of.
I only use the chart in the Coinbase app so this discrepancy did not make any sense. I decided to double check the chart for the time I bought, and sure enough, it wasn't even close!

As you can see in my screenshot above the price of XRP was $0.61 usd per coin at 10:47am eastern standard time according to Coinbase's own chart, but my transaction confirmation shows $0.65 per coin at this very same time.
As far as I know Coinbase doesn't charge a fee per coin , or any fee for that matter when converting from one crypto currency to another on their mobile app.*
I know this for sure because I have been using their service for three years now, and the only time I get charged a service fee is when I buy using my debit card.
I did contact Coinbase asking for an explanation , and I got an automated service ticket response that says they are a little backed up , but will get to my request. I still haven't heard back from them yet, but it usually takes at least 24hrs for their support staff to respond.
In the meantime I am going to go back through, and check my previous transactions to see if there are any more discrepancies.
If anyone else has had this happen to them please chime in! I'm hoping it's just an oversight on my part, and not something more sinister!
Please comment below if you have experienced anything like this with Coinbase, and if so did you get an explanation as to why something like this could happen?
*Disclaimer: I am not accusing Coinbase of ripping me off . I am just confused as to how this could happen, and hoping someone could explain since I know I won't be hearing back from Coinbase support any time soon. I am also wondering if it has happened to anyone else?
UPDATE 1 : Yes they do charge a fee, and apparently I didn't read well enough!
It is listed in the TOS here :

There are some issues that I have to address though. The reason I thought something was wrong is because I have been using the conversation feature for quite a while, but this was the first time there was such a difference in the price that I actually noticed it. In this case it was almost $0.05 per coin.
The reason for this is that Coinbase uses the chart from Coinbase Pro to process this "margin spread" , not the chart you see on the Coinbase mobile app.
I think the best way to avoid this in the future will be to only use the chart on the mobile app as a guide, and not to execute any conversions without first checking the chart on Coinbase Pro.
I have been using Cryptocurrency, and Coinbase for three years now, and I'm still making costly mistakes! Hopefully this post will help others avoid my rookie mistakes!