Wrong buys of what, credits or views of pages?
Credits get used up eventually, so are not wasted, unless you run out of time. With practice you get better at guessing from the meagre details in the index which entries are more likely to be relevant, but you do sometimes have to look at a lot of toads before you find your prince. Sometimes your prince seems to have married perfectly legally, but was never born and never died (even when his wife remarried a few years after his last recorded census appearance. I think he is under the patio).
There is a law of diminishing returns too, so the more you find out the fewer of the ones that are left belong to your lot. Never throw anything out, though. Save it or print it out and file it under "Maybe". A link may surface in the future. And keep a note of the pages you didn't find anyone at all of the right name on, to save you repeating the same fruitless exercise.