Sure you still have the right to complain. If I didn't ask for it, and didn't want it, and you give it to me anyway, I'm under no obligation to be grateful for it, especially if there is something wrong with it.
If I come to your store to buy a lamp, and you decide to also give me a free pair of sunglasses, (that I never asked for), and they break, guess what, I have a right to ***** about it. "I can see why they gave them away for free, because the things are cheap pieces of crap that didn't last 30 minutes!" etc etc.
The quality of the free thing is very important, as well as whether or not it was even desired. I frequently turn down free stuff, because I don't want it. A lot of people are of the mindset that if it's free, it's good to have it anyway. I disagree, if I don't find the item to have any value what so ever, all it does it clutter up my place. So keep your stuff thank you, if I want it, I'll let you know.
Now, if I specifically ask you for something for free, "Hey man, can you pick me up something when you hit the burger joint? I'm starving" Then no, I don't think you've got much of a right to complain. I mean, you can, but it will look more like you being a dick. But if I don't specify to you that I don't, for example, want onions on the free cheeseburger you are buying me, I"m not going to ***** about the onions. I'm perfectly fine with taking the onions off, and eating my burger that I got for free, because I asked you to get it for me. But if you get me a burger, and I never asked you for a burger, and I am not hungry, while I will personally thank you for the kind thought, I'm not going to eat your burger.