Buying properties at Philadelphia Sheriff's Sale is risky business. First of all you are buying blind. You can't see inside the property. Make sure you know values and have experience looking at condition. You don't want to bid more than 60% of market value.
Then there are lots of details that would never come up in a traditional transaction. Is it a mortgage sale (most properties are postponed or purchased back by the bank) or a tax sale (subject to a 1-year right of redemption.) Make sure you have a good title company who will insure the deed. Make sure you are buying with Cash or Hard Money because you can not get a mortgage on a Sheriff's Deed.
It is a gamble so be prepared to walk away from your 10% deposit if the deal looks bad but if you know what you are doing and you are lucky you can WIN BIG!