pitfalls for tax sale

[Bonnie Y.]

I'm close to making my first ever investment purchase, which turns out to be a tax sale. I thought the only downside is I won't be able to cash out on it during the redemption period.  Now more and more questions are popping up. Here are a couple.

1. Supposed I put in $50k on the renovation of a property which I bought for $30k, if the seller decides to pay off the tax and buy back the house, does he pay $30k or $80k plus interest/penalty?

2. How often does it happen that the seller actually come back with cash and buy back the property?

3. Are there any other pitfalls before I get clear title on the property?

Thanks, BP community!