Next big part comes into play, what if any fit guarantee comes into play? If the item arrives, does not fit right, who is responsible for making it right as well as who covers shipping as well is there a point where it is decided it is just not worth it.
Body awareness also comes into play. With custom pieces it is easy to try and pattern one piece to different measurements but it just does not work. Especially for fitted garments, there are definitely certain lines that come into play and if the proportion ratios shift too much, the look just is never there.
I personally have seen some custom pieces take four months to get completely resolved satisfactory. In many ways, off the rack and having a solid tailor to really fit the piece is far better.