Do your due diligence.
Most people that aren't familiar with your situation or the area aren't going to know if it is a good deal or not. I have made and have had clients make tax sale purchases that have worked out tremendously. Others not so much.
Do the research.
@Delonte Wall isn't the DC tax sale over? I thought it was last month.
Certainly buying an 8 unit building at tax sale can be a good idea if you can get it cheap enough. $11,000 is certainly cheap enough. However $11,000 is most likely the starting price, not what the property will ultimately go for. Since it is an auction it is likely to go for Much more. It could easily go for $500,000+ depending on where it is.
DC changed their tax sale laws a few years ago. You need to know the rules and what you are buying. Are you buying a lien against the property or are you buying a tax deed?