Look through the guide archives. You'll find some useful stuff there.
Be careful buying any on guide sales. Most of them are well-known, and variations have been posted for free elsewhere. Be sure that a moderator or trusted poster verifies.
Take care, do not trust every guide. You can lose mils with this.
Or someone tryed to make a guide, and say his item will sell good,
anyways he tryes to sell his own item, because he cant sell it.
And yeah, in the archives you can find some good ones.