Is this high school or college?
It’s situationally OK to trace or copy things in school as part of learning exercises, as long as the instructor specifies that copying is part of the assignment. For example, when I was in design school, we were assigned to trace thousands of letters from magazines as a way of familiarizing ourselves with typography. Painting and drawing majors often went to the museum and drew from the works hanging there for much the same reason. On the other hand, I remember a star student in our senior level design class being permanently expelled from the school for copying an ad from a magazine and turning it in as his own design.
It’s absolutely not OK — ethically or legally — to trace or copy things if the plan is to use or sell those copies commercially. In a real-life work environment, plagiarism is often a firing offense since it puts the employer in legal jeopardy and undermines the credibility of the business.
What do you mean by a vector? Do you mean a logo that’s built with vector outlines? Is this a for-sale logo found on a website somewhere? Would it be an exclusive sale where they would remove it and not sell it again if this hardware store bought it? Or is it just a logo-like object that was found on a download site? The end user license agreement (EULA) on most dowloaded commercial art specifies that it cannot be use as a logo or a part of a logo. Your friend would need to check the EULA.
If it’s just something he found and wants to steal by copying, that’s wrong and, as I said, illegal. There is no agreed-upon amount something needs to be changed before it’s considered changed enough to not run afoul of copyright laws. Most anything that looks as though it’s been copied and changed is pretty much fair game for the original copyright holder to sue.
With logos, the usual practice is for the copyright holder (the designer) to transfer all rights (including the copyright) to the buyer. A business owner would be stupid to allow someone else to maintain control over something as important as the company’s branding.