It is possible to limit the minimum and maximum split of the subnet that you bring to the IP Address Marketplace.
By default, the maximum split size is set to the block size of your subnet, while the minimum split size is set to /32 (a single IP).
This means that the customer can order any block size from your subnet.
If, for instance, you would like to avoid fragmentation of your IP address range, you can choose a larger minimum split size, like /24 - in such case. This way, it will only be possible to order a /24 or a larger block.
Similarly, if you would like to prohibit certain maximum block size, you can specify this via maximum split size. For example, to avoid monetisation of your whole IP address range, let's say - /16, you can configure maximum split size to /17 or lower.