Lets face it,dealing with someone you have never met,you can't see and know nothing about,is a little scary.  There are some steps you can take to protect yourself from the unscrupulous seller.  A lot of the auction sites today provide various insurance policies for the patrons.

E-Bay has the Safe Harbor program which insures your transactions up to $200.00 with a $25.00 deductible,it is free.
Amazon.com, Yahoo and others also have similar programs.

A little groundwork and common sense on your part will go a long way in protecting yourself.  Most all the auctions today have a "feedback" system with which you can check on a buyer or sellers track record.  Take a look at the buyer or sellers feedback and see how they have performed in the past.  Did the buyer send the funds quickly,were they fast to reply to e-mail notices, as a seller,did they ship promptly, was the merchandise as described, how was their packaging.
This will give you a real good indication of who you are dealing with.

It is commonplace for sellers to request payment prior to shipping.  Of the many ways to pay for your items,the credit card is one of the safest choices.  Checks,money orders and cashiers checks provide no recourse if you have been swindled.  They are a last resort but there are a lot of sellers who are not setup for credit card purchases so there will be times when you must use other forms of payment.

Several on-line pay systems are available that allow you to e-mail your payment thru a secure enviroment.  We are using them with a great deal of success.  Buyers do not have to wait for checks to clear and sellers have payment within minutes and are able to ship the same day in most cases. I like the fact that you only give your credit card info out Once,at signup. From then on it is recorded so you simply exchange funds with no additional credit card information exchanged over the net.
Excellent security=> PayPal. will Pay You $5.00 for signing up and for all the buyers you signup you receive an additional $5.00


For any large dollar purchases I recommend you use one of the "Escrow Services" available. These are third party services who act as a middleman for the transaction. 
They hold the money until you receive the merchandise and if all is well they release it to the seller.  Sellers are protected as they do not receive the OK to ship until funds have been verified.  Charges for these services vary from 3.5- 5% of the transaction. 
Several are=> I-Escrow    SecureTrades

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Now, armed with the tips that I have provided
go find that special item you need to fill in your collection and remember

"Be Careful Out There"