Can't Cut the Mustard
DEFINITION: If a person "can't cut the mustard," he is somehow unable to meet requirements or expectations.

EXAMPLE: I know he used to work for our competitor, but he just can't seem to cut the mustard as our VP of Sales.
"I am currently writing several papers for conferences and journals, and I will soon need your help and support again. I am very satisfied with [my editor's] expertise and kind concern. I will recommend your website [to my colleagues] as an excellent proofreading and editing service. Thank you again for your help. "
Min-Seok Cha
KAIST Graduate School of Management
Seoul, South Korea