What ever you do, you must keep in mind that you deal with reality. There is a lot of mimicking of things in witchcraft, but when it comes to materials or offerings, quality is important. Perhaps in Greek mythology, they excuse leaving bones to gods by stories of cheating them with stack of bones covered with skins, but here you offer the part from your good things. I find it very hard to accept that you cheat the powers you work with, like make mock-offerings or give them fake money – Chinese might have that, but I don’t follow their traditions and so I do not.
Co-along with that I would say that you do the same with spell crafts. Why make a mockery of your art if you have the ability to remain honest with it? You can replace things in the spells if you don’t have something, but it is incredibly stupid to put peppermint in the spell and call it nettle. Honest mistake is one thing – mistakes happen and the powers you work with will understand – but deceiving is a whole different level.
The quality of the things you use in your craft is also what will make difference between failing and succeeding. If you decide that “Naah, this 4 year old spiderweb is good enough” while you can go and harvest a fresh ones, then well – what are we talking about? Yup, I have gone and done it in the past. Both gathering the webs and used something that was out of date. There is a difference and I learned that it is easier to keep your stocks in order and learn to use things over time rather than have something sit and let them go out of date.
However, knowledge is never out of date and improves with time. 😉