I've just looked back to see what your visa situation is, and find that that doesn't come into the question because you have an open visa anyway.
This is just a matter of good manners - don't verbally accept a job (even without signing a contract) and then, within the next short time, think it's all right to tell them no, you don't want it. If you want to delay the answer as you may be getting a skilled offer, say so. NZ has a small population, and someone who messes employers about can get themselves a poor reputation quite easily - if word gets around that you're not a serious prospect, it may be that when you actually NEED a low-skilled job, you won't be considered.