On a lot of jobs, retouching can't start until the client says which photos they're keeping. The problem is almost never the choice itself, it's how it reaches you: an email full of numbers, a follow-up the next day that changes two of them, a screenshot marked up by hand. You spend more time rebuilding the list than editing.
The real cost: decoding a scattered selection
A selection that arrives in pieces forces an invisible, tedious job: cross-checking file numbers against your previews, guessing whether "the third one" means the third on the contact sheet or the third from the end, handling the client who replies twice with two different lists. Every round adds delay and multiplies the risk of an error, meaning retouching a photo they didn't actually want.
Let the client mark their favourites on the delivery
The selection sorts itself out cleanly when it happens where the photos are, not in an email thread. On xFer, you deliver the full set of shots on a page in your name, and the client marks their favourites directly on the images they want to keep. You get a single list, tied to the right files, with no numbers to transcribe.
The client has nothing to install or figure out: they open the page, click the photos they like, done. What used to take three email exchanges happens in one session, at their own pace, with nobody retyping anything.
Frame a single round, and announce it
State clearly, before the selection, how many photos are included and that you're expecting one final list. A client who knows their selection triggers the retouching takes the time to do it in one go, instead of sending a choice they revise three times.
This selection step pairs well with a two-stage delivery: a first teaser to calm the wait, then the full page where the client marks their favourites before you retouch the final selection. Each keeps its role, and nobody chases a list buried in an inbox.
In short
Photo selection belongs on the delivery page, not in email: the client marks their favourites on the images, you get a tidy list tied to the right files, you deliver the final retouched version. One round announced in advance, and you get back the time that decoding numbers used to steal.