There are some risks if she is drop-shipping the item. (ie: She lists on ebay, the item sells and she receives payment. She then forwards the shipping information to the supplier, who ships the purchased item directly to the buyer, and pays the supplier directly).
What can go wrong is, in the event of a dispute (item not received, item not as described, item damaged, etc), payment is reversed from her PP account back to the buyer who is also protected by eBay+PayPal buyer protection; She then needs to open her own dispute against the supplier - but she isn't similarly protected; it also depends on how she pays her supplier.
The fees for selling on ebay.com however is also quite high - it's actually closer to 20%, and this excludes postage.
Most fees on ebay.com are apparent, but some aren't that obvious. You'll need to build them into your selling price.
1) Ebay listing fee (50 free per month, starts at USD0.10 and up)
2) Ebay final value fee (10% of the total sale amount, capped at USD250)
3) Paypal fees (USD0.30 + 3.4%)
4) Paypal exchange rate (3.5% spread; Paypal's withdrawal rate right now is USD1 = SGD1.22415. If you had USD currency and walked into a money changer right now, their rate is USD1 = SGD1.2520 instead. The current interbank rate is SGD1.25675)
5) Paypal withdrawal fee. SGD1 if you're withdrawing less than SGD200.
If she isn't drop-shipping, there is the additional cost of shipping:
6) Packing materials (envelope, and any additional materials to protect the item if necessary)
7) Postage cost (starts from $3.30 for registered mail to most countries)
8) Time and travel cost to visit a post office to ship your items.
If you're selling on ebay and/or accepting payment with Paypal:
a) Always ship with tracking (registered airmail). If you ship without, any buyer can reverse the payment with an 'item not received' dispute; and you will get a *lot* of that.
b) Only ship to the address on the paypal payment, or on the ebay transaction only. Shipping to any other address will allow the buyer file a successful 'item not received' dispute, and get their money back.
You might also find the following useful if you're planning to set up an 'ebay business'.
a) If you plan to sell on ebay.com, seller reputation matters. If you've a new account, expect your auctions to close slightly lower price than other more established accounts selling an identical item.
b) Build the occasional loss into your prices. Once in a while you'll get scammed, or become a victim of feedback extortion. It may sometimes be better to just eat the loss, than to get hit with negative feedback.
c) Check ebay prices, find out how much the item you plan to sell has been closing for, and from there you can determine if it's worthwhile for you to sell on that platform.
d) Beware of buyers who offer to trade outside of ebay. Reasons for that alone can fill another post as long as this.
but you need to know what item is hot 
