If the seller and agent are serious about selling the house, waiting for a better offer seems like the only reason (aside from some other unforeseen family circumstances) that they would delay responding. 

The home had several unforeseen issues (leaking roof, mold, etc) that made my renovation costs go up.

My guess is that it was a combination of 'wait and see' to ensure there wasn't anything goofy going on with the property (IE we had the chops to do it right and keep a tenant in and cash flowing), but also simply our track record and credibility with owning and managing rentals, in general - at the time was a tougher sell.If capital is limited, that's fine but I guess I'd make sure you have that figured out BEFORE moving into this world - you obviously need to have enough to get through the project but you need enough to absorb the period above as well as any unforeseen stuff that can come up.

Making sure you’ve read through and understood everything in each document will keep you from being surprised by unforeseen risks orunfavorable terms.

As for unforeseen expenses on the sewer line, the only unforeseen you could have is if the portion that is in the street that connects to the city’s mainline to your line, if that section is bad, you will need to replace that section as well which is almost as costly for a much shorter length.

I know this is a very broad question and in fact, I'm just looking for anything that comes to your mind that might help me avoid unforeseen risk or headache.Worse case scenario, if the buyer defaults, what is the the foreclosure procedure like and how much should I budget for that? 

I should mention I also have lines of credit and investment accounts in case the $10k isn't enough to cover some unforeseen calamity.

The home owner in their haste to enjoy the unforeseen windfall, became oblivious to the lurking storm. 2008, the economy tanks, hundreds of thousands lose their jobs.

I had the inspection done and some unforeseen issues were discovered--nothing huge, but things that will have to be addressed before I can proceed with my original plan for a value play. 

Then he stated that he had started to use his own monies to pay some of the holding costs because the holding period was longer than anticipated and he wanted me to reimburse him for those costs because it stated in my portion of the agreement that I would "provide additional investor monies if needed to cover unforeseen expenses."