Yep, been there in my novice days.
Not with pc world, but another shop, One of my first up-grades, decided to get a cd-rw, and in the shop I could see on the box cd-rw but wasn't sure wheather it ment that it could read rewrite or wheather it ment that it could record as well.
So asked the shop assistant, who I ended up with having a in-depth discussion on the benefits of being able to store large amount of data on cd and yes it would do that for me.
Got home (on the other side of town) opened the box, read the instruction manual which informed me, that no it didn't record data ahhhhh. But to add insult to injury, when I dashed back to the shop, and asked for my money back, I was told that because I had paid on my husbands debit card, and I only had my debit card with me they could refund my money!!!!!! Even though the only difference in the cards is the name everything else matched. Was I turse or was I turse but it worked once I spoked to the manager, explained that my card belonged to the same account as my husband, and if they expected me to drive back across town and return with his card, when they gave me the wrong information then they were going to pay my petrol money and time as well has the refund. Worked a treat.