MOP : Character Re-customization

Greetings everyone!

I'm planning to purchase the Character re-customization service but i'm having second thoughts because there were open threads in this forum wherein they had issues during the customization. Most common issue is that they were getting an error "Could not customize character" when they try to apply the changes. Unfortunately, no one responded with the solution on these posts. Any idea on how to fix this just in case if i encounter such issue? Any advice is greatly appreciated.

Thank you,

P.S. This is for MOP.