If you sign up for Paypal they cover purchases up to £500.
If for some reason the item you purchase is not as described, or faulty, and the seller won't refund the money then you can claim it back.
It doesn't happen instantly as Paypal have to first contact the seller and hear their side of the story.
If you use your credit card to make Paypal purchases then you get the added protection that your credit card offers also.
Never send cash or pay using one of the money exchanges.
ebaY is safe and can be great value, here are some tips
Make sure you ask any(all) questions you have about the item for sale before you bid.
If sellers avoid answering your questions, or don't address them exactly then forget it, there is a reason they are doing that.
Try and read between the lines as some sellers will be real sneaky about the way they word their descriptions.
Watch out for new, mainstream items sold quite a bit under the lowest High St value you can find on-line. It would be very difficult for most small businesses to buy in large enough quantities to warrant much cheaper prices. Be careful that they don't sting you with grossly over inflated postage and packing charges to make up the price difference.
If a seller claims to run a business and they are charging v.a.t. try cross referencing their postcode and address to see if it really is a genuine physical address.
Remember If it sounds way too good to be true, then it probably is.
Also worth mentioning is that ebaY customer service is appalling. If you have a complaint the only method of contact is by email and they usually take a while to reply. The only people that get to speak to actual employees are power sellers who get a direct line phone number.
Hope this helps