If its a recommendation from someone you trust, sure.
I'd say look around and compare rates and brands. Obviously specialty stores for car audio would be your best bet for whole systems. Obviously customer reviews and consumer reports are handy as well (never take the salesman's word for it--they're trying to sell whatever they can to you.).
Essentially you want to be sure of its specs both performance wise (efficiency, heating, power it draws, its radio reception range, sophistication, simplicity or complexity of controls etc. etc. etc.) and its physical specs (Are you getting a standard size replacement or do you have to remodel the interior of your vehicle? What are its hookup requirements? etc.).
Speakers you want to consider their drive and power requirements, their housing, and their output quality regardless if you just want a new regular system or one of those torrential sound hurricanes. After-all, why get a new system if its speakers sound like complete and utter $***?
You might also consider an RF choke/filter kit. Unless your system specifically has it (or some other kind of electronic filtering) built in, you might need one. This is important to eliminate the "noise" from the alternator and adjacent devices for the interior of your car. Pretty simple, really.
I'm assuming you're not an electronics nut like I am.