Common speech and, often, writing use the verbs "can" and "will" interchangeably, which one should not. They don't mean the same thing. "Can" refers to ability. If you can replace "can" with "is/are able to" and the sentence still make sense, then you're using correctly. If you refer to possibility or permission, then you've used it incorrectly and should swap it out for "may." If you refer to intent, not ability, then "will" is the proper verb. If you're referring to obligation, then use "should."
The above two buyer requests were recently posted on Fiverr. I did not bid on either one.
Let's dissect the first (the one on the left).
Project Scope - Ghostwriting
Length - 9,000 words
Deadline - 3 days
Budget - $5
This project will take about 30 hours to draft, self-edit, revise, and format for delivery. To complete this project in three days, I'd have to put in at least 10 hours a day for three days. The deadline does not include time for the client to review the drafted story or any time and effort needed to revise per the client's feedback. I don't know about you, but I can't write for 10 hours straight in a single day.
Can I produce 9,000 words of decent copy in three days? Yes, as a matter of fact, I can.
But I won't.
Let's look at the second request (the one on the right).
Project Scope - Editing
Length - 24,024 words
Deadline - 5 days
Budget $5 - $10
This project will around 16 hours to complete, so can I complete the project within the deadline? Yes. But I won't.
When writing a request to hire a writer or editor, be cognizant of what you're asking. If you post requirements that are unreasonable (e.g., writing 30,000 words in three days), then you're doomed to disappointment. If you post unreasonable budgets, then don't complain when you receive delivery of substandard and/or plagiarized work.
Just because I can do something, doesn't mean I should or will.