Hello and welcome to UO!
1) That depends. Generally that's not possible. EA has a special service that offers extra security (it costs a bit, but safety above all, eh?), you can read more about it here:
http://support.ea.com/cgi-bin/ea.cfg/php/enduser/std_adp.php?p_faqid=6174
2) That depends. Most deals are pay first, receive later. When you pay via PayPal, PayPal will offer you some sort of buyer protection. When buying an account it's good to check out their reputation and history. Some big brokers sell accounts, they are more expensive but more reliable. When buying from a player you should google him and do some research and ask him some general questions about the account, just to make sure it's not a hacked account or anything.
3) Unlike WoW and some other games, EA does not have a rule against purchasing accounts, items or gold for RL cash. You will never get punished solely for this reason. If you buy loads of cheated items (10 'unique' event items and 100 barbed kits) you might find yourself in trouble and get your items deleted. If you are buying from a reliable person you will never find yourself in trouble. The key is: ask around. Just PM some of the big traders and they can usually tell you unanimously who can be trusted and who can't be.
I'll add in some extra advice (whether you like it or not
): you might want to consider not buying an account. Just buy some gold and a few advanced char tokens (these tokens give you some pretty high skills for more info see here:
http://www.uoguide.com/Advanced_Character_Token). These tokens cost $29.99 at the official (uogamecodes.com) website, but can be purchased for a lot less from players (I sell the tokens for $12 personally).
Skill training is part of the fun and you get to know the game a little. Buying an account with 5 fully done chars will allow you to do everything, but you will not have learned how to properly use the skills, nor do you get to know the lands, as you do when training. There are many online guides (on Stratics and forums like
www.uoforums.com), which explain you how to train. And should you run into problems, the boards can always help you out. Plus you will save a lot of money.
I can imagine taking the easy road and buying an account, but training skills will give you a bigger sense of satisfaction I believe. You can be proud of what you have achieved.