I don't trust anyone with access to my systems unless they are someone I know well, watch everything they do, and have a full backup of the working system (and a way to restore it) to hand.
Too many times I have seen someone come in to install some software on a soon-to-be-live system and mess things up. Scenarios like this were all too common:
Software Supplier: I need root access to do this.
Me: No. Tell me what you need and I will do it.
SS: It is complicated...
Me: I know what I am doing. Tell me what you need.
SS: I have to do it. I need root.
SS: I will speak to your manager.
Manager: He said no.
SS: I will speak to the Project Manager
PM: I don't understand any of this stuff. Let them have root. What harm can they do?
SS: "cd /usr/bin"
SS: "cd /homer/pi" (sh: cd: /homer/pi: No such file or directory)
SS: "rm -r *"
SS: Why is "vi" not working now?
Me: Pushes SS out of the way, starts restore of /usr/bin. Emails manager and PM, and yes, same scenario happened on another system some time later.