This happens to me quite frequently.  At least it did when I signed up and implemented the Melio billy pay system to my clients QBO.  If I wasn't constantly reviewing the Balance sheet then I wouldn't catch the constant changes that Melio makes to my books.

First I asked if they would map their charges to a bank service charge.  They said that was impossible and then they randomly created an expense that had nothing to do with service charges and place it on the Chart of Accounts each time a transaction was processed.  I had to screenshot and copy and paste because their customer service didn't believe me.

Then when I review the bills that I've paid I'll see that the balance is different than what I created.  When I review the bill there is a charge or credit by Melio saying that it's to balance something in the system.  That is scary.  If I tried to explain that to a client they wouldn't know what I was talking about or think I was being honest.  They would probably think I'm making excuses about why the balance is off.

Last, when I first signed up the customer service rep that was assigned to me was extremely cocky.  I called him out on it and he passed me over to someone else.  Whenever there was an issue with implementation he would tell me not to worry about it or wanted me to tell my clients the same - not to worry about it.  That I'm taking it too seriously.  Then he tried to get me to be apart of a program where I'm basically giving them constant feedback about their product.  So I would be a test client and they wanted all of the information for my existing clients. 

If it wasn't integrated into QBO I wouldn't have tried to make it work so much.  I'm not getting as much issues as I did last year.  But their fees are very high and I usually have to bypass their system and pay directly with the vendors.  Even though it's a "free" system the fees to send out checks is $1.50 per check and the credit card fee is high so my clients are not happy with that.