How Do You State Your Mind Without Sounding Ungrateful?

When you buy something you have high hopes for it, but it breaks or doesn’t live up to your expectations?

What do you do? Do you contact the seller? The store? The website? And what if they help you and send you another for free? Even if your product isn’t new but an old one bought from eBay? And what if you’re disappointed in your new one?What do you do?

Email them? Tell them? Come off ungrateful after what they went through to help you. How do you state your issues without sounding like a bitch who can’t be made happy regardless of what they do to appease you?

I don’t know, but I’m stuck with something that doesn’t fit and I could sell it or somehow change it so I can make another one but I can’t find something similar to change it to.

So, what do you do in situations like this?