This has been a frustration for us also, but we tend to accept graciously and complain (out of DS's earshot) later.

: FIL and wife are the worst offenders. They find these "great deals" at close out stores and garage sales. Well, you know what? So do I, BUT I make sure the toy is first developmentally appropriate for a 3 year old and... isn't in some state of disrepair. DS has spent many a day loving and hating the toys from Grandma and Grandpa. That big ol' LOUD train set (made for a Christmas Tree I think) is really neat
looking. However, it only works half the time and when it cares to do that much it spends most of the time falling off the rails which of course Mommy has to fix every 4 or 5 minutes. It's excruciating for us all. This is only one example and the worst of the lot, but we've had many lovely LOOKING trucks and cars given to DS only to have them fall apart in days and of course, DS is crestfallen, yk?

The train put us over though. We did later contact DH's Dad and explained that while we do very much appreciate the thought, we'd be very grateful if he just checked with us first about big things or things perhaps DS already has a version of. Our home is very small, and with the train fiasco, we were even more frustrated that we had just spent actual money on a very special train set for DS that we'd put a lot of thought and care into--age appropriate, usable by hand rather than electric/battery. We don't have a lot of money so it was a big deal. When Grandpa introduced the MONDO TRAIN (with a bell and whistle you can't turn off btw

), it felt like a slap in the face. Especially considering that it hadn't been a week since we'd told him about the one we'd bought for DS.

In the end, FIL understood and promised to check in first. We expressed our deep appreciation for the thought and I think did a good job of not making him feel badly for just being excited to give DS what he knows DS will like, but now we have confirmation that we won't end up with more well, CRAP so I think it was important to speak up.
On gift ideas, we tend to be open about this. Everyone does know that DS adores trucks and we've told everyone that he has plenty for now--too many actually. Last birthday, we had a theme: art supplies. I didn't want anyone spending too much but I knew they would want to give him a gift... so
A box of crayons,
A reem of construction paper, etc. Very simple, nice and oh so usable! Since DS's birthday is right after the holidays, I do imagine most were relieved that I insisted that they keep things to a minimum.