Market orders are restricted to the region they are in. This allows for inter-regional trading (buy at Jita, haul to some far away place, sell at a markup).
The Trade skills allow you to:
- have more orders set up on the market; just a few levels trained in the Trade and Retail skills extend the default 5 orders to 50 - 300+.
- pay slightly lower taxes.
- make changes to your market buy/sell orders without having to actually dock at the station where they are (remote config). This is very useful if you don’t want to go to Jita, you can stay in a nearby system and still manage your Jita trading. Also very useful in null-security space, where the owners of the space can block you from docking at their station (you can go to a nearby system and still manage your sale orders in that station).
- buy and sell orders are always visible within the entire region, but there is no teleportation, so the actual buying and selling must happen IN the station where the stuff is, and someone has to transport it there for the transaction to happen. There are no choices for sell orders, you’re selling your stuff WHERE IT IS. But there are trade skills that allow you to buy not just from a station, but from the vicinity, even from the entire region. This lets you blanked the region with a single order to buy minerals, for example, but instead of the sellers having to haul the minerals to you before they can sell to you, YOU will have to go pick up all the quantities of minerals that you’ve bought all over the region.
Contracts are visible everywhere in the galaxy, but you still have to travel to the station where the stuff is, to pick it up. No teleportation, someone must do the hauling.
Other differences between contracts and the market are:
Market require items to be repaired to full and “repackaged” in order to be sold. Repackaging a ship will remove all the modules in it and destroy all the rigs it has. Contracts allow un-packaged fully fitted ships with rigs and modules to be sold as they are.
Market only allows un-modified blueprint originals to be sold. Contracts allow researched/improved blueprints, and blueprint copies, to be sold.
With the market, only the best priced item at a station will sell, every other order must wait for the best priced to be sold out. Contracts allow you to choose which contract to fulfill, regardless of price, and including scam-priced contracts. Contracts can also be set up as private, where only a corp. or character can see the contract.