There are certainly a lot of stories in various internet fora about Ambrosi's terrible service, very long wait periods, the wrong details in the trousers and so on.
It seems that if you order his trousers through a trunk show held by an intermediary, such as The Armoury, you will get your trousers quickly and with no problems at all. However, if you order from the man himself, you are taking a chance on pain and disappointment.
Here's another anecdote (this one from only six years ago now) from an Australian menswear blogger:
The final installment from men's style writer Andrew Doyle about his bespoke trousers from fourth generation Neopolitan trouser makers Ambrosi.
www.timelessman.com.au
His trousers took a year to arrive, instead of a couple of months, and were too tight on him as well.
But, despite that, he still considers Ambrosi to be "a friend" - even though he only spoke with him twice and feared that he would never actually receive his expensive trousers!