I know it'd be tacky to do so, though if like the LW of the story if one is that focused on gifts and what the guests can reciprocate to the festivities, then there should be no beating around the bush on the matter. If you don't want to put right up front on the invitations that X amount is being spent on each person and if that can't be met, surpassed or at least come pretty close, the guest is encouraged to decline, then do so by word-of-mouth. That way your wedding has a better chance of being how you envisioned, free of cheapskates and deadbeats
If you cannot see yourself doing something like that, enjoy the wedding and don't worry about what so and so's getting you. With the exception of the taking the dogs to the vet *gift* from the ILs. It was not very nice to use it as such.
It would also seem to me that gift givers should be wary of ‘hiding’ money in the gifts. Sure, it’s clever, amusing, and fun to do so, but only if the receiver finds the $$! Not everyone is going to think to look in all the nooks and crannies of gifts for money, because they’re probably not expecting it to be there, unless they know the giver does that sometimes. That’s a lot of money wasted, or ending up in the hands of people who weren’t supposed to get it.
I agree with the hiding of money is not the best idea. I always think of that story I've heard many times (not sure if real or like an urban legend) where a son was graduating from high school and for a gift, he'd wanted a car. So he and his dad went to shop around and look at different ones, and the son found the one he liked. On graduation day, for his gift, his dad gave his son a Bible. In his disappointment, he threw the Bible down and stormed out of the house not to return and he and his father didn't speak for years. I think it was the dad died and the son came back and while going through his dad's things, found the Bible and opened it. And there inside was money in the exact amount of the car they'd chosen long before.