When an offer is accepted but includes an addition or deviation, the agreement is established provided the change does not significantly alter the conditions of the agreement and, at the same time, the offeror does not reject it without undue delay. The purpose of this rule is primarily to forestall doubts whether the agreement was concluded in cases where there are no compelling reasons to doubt whether it was in the parties best interest to conclude the agreement with modified acceptance. This rule, however, has its drawbacks. When an offer does not exclude modified acceptance and the offerer fails to reject it without undue delay (for example, because it fails to note the change), the parties risk a dispute over whether or not the change constitutes a significant change to the offer. Does changing the purchase price by only 0.1% constitute a significant or insignificant change? The degree of risk is greater since the matter would typically end up being considered by the courts.
In this respect, we should also pay attention to a new institution known as subsequent written confirmation, which will only apply to agreements between businessmen that are not in writing (it is worth considering whether this rule also applies to agreements concluded via email without an electronic signature). If one of the parties subsequently sends to the other party in good faith a written confirmation regarding the contents of their arrangements, then the agreement – provided the other party does not reject it –would be concluded under the conditions stated in the confirmation even if they slightly deviated from the original arrangement. It is interesting that in this case the law qualifies an admissible deviation as a deviation “that a reasonable businessman would still approve”. Nevertheless, it seems this principle is the same as in the case of modified acceptance.
We can thus generally recommend always considering whether or not to exclude the option of modified acceptance from the offer. However, if you wish to reduce the risk of being unpleasantly surprised, always be sure to read carefully what comes in the mail (including e-mail).