Incorporating will help insulate you from liability, but there are ways around that for the determined plaintiff and the creative lawyer. A well worded warning or exculpatory notice [what is sometimes referred to as a "waiver", erroneously] will also help, but there are limitations to how much that will insulate you from liability. The law of product liability is different according to which jurisdiction you're in, but there should be a distinction between a defective product which does not perform as designed and injures someone as a consequence, a dangerous product, which performs as designed but has inadequate safeguards against injury, and cases where the operator injured himself because he misused the product or exercised insuffuicient care. You have to try to fit within the rule best summarised by the maxim, "volenti non fit injuria": voluntary assumption of risk, but even this may not provide protection against the remote user: ie, the recipient of a present or a resale or the guy who says, "Hey, nice custom folder! The maker said the lock was as good as any production knife?Did you see that Cold Steel video? I guess I must be able to backslash and break this brick with this folder... Hey Bud, would you help me find my fingers?"
The best you can do is take reasonable care to ensure the product isn't defective, which I'm sure everyone here does anyway, give each customer a little written waiver/notice, [which, ideally, they should sign], covering all types of potential problems: "knives are sharp and dangerous and require special care so use at your own risk and try not to be a moron and you agree that I'm not liable for any reason including my gross negligence, even though I never should have let an idiot like you within a mile of my knives", but in much more detailed and proper legalese, incorporate if you can afford it, get insurance, if possible, and befriend a lawyer who works cheap, if you can stand it.
In other words, you can't really protect yourself completely, the cost of trying to do so is ridiculous, but doing some simple things might help.