VAGUENESS
Some terms in a contract may be so uncertain because they do not provide enough details. For instance, the terms do not clearly show who is supposed to do what and how much is supposed to be paid. Courts may say that the terms are too vague to be enforced. Expressions that are difficult to understand/interpret (such as "the finishing must be beautiful in my eyes") should be avoided.
INCOMPLETENESS
There may be no binding contract if the agreement is incomplete. For example, important terms such as price have been left out.
EXEMPTION/EXCLUSION CLAUSES
These are terms which one party includes trying to avoid responsibility to pay compensation for any loss, injury or damage to any person or property. These are usually for negligent acts. Such clauses may be found in notices, or in small print on receipts, order forms and written contracts. Whether such clauses are effective to help that party escape liability would depend on certain factors such as: whether the clause was properly brought to your attention before or at the time of contracting, or whether such a term is "reasonable" under the Unfair Contract Terms Act.