On both islands there are two property markets, 'Local' and 'Open'.
On Guernsey, most properties are in the ‘local market’ meaning that they can only be rented or bought by locally qualified residents or ‘housing licence’ holders. If you are not from Guernsey, your employer will have to obtain a licence for you.
On Jersey, only people from the island originally (or those that have lived there for many years) are able to buy and rent from the local market. Firms are allocated a number of rental licences per year dependant on their headcount. Firms then allocate them amongst employees at their discretion thus allowing them to rent property normally reserved for the local market. Buying is still tough without having lived on island for a considerable time.
On both islands, the open market properties tend to be more expensive to rent or buy and are usually found in less attractive locations.