They will burn the carpets with irons, put deep, deep scratches into any hard floors. 

Old cast iron pipes suck.

It was ironic that the same day he was posting those pictures he also posted a video on Instagram that said it was shot in Portugal. 

You definitely want to strike while the iron is hot and get the deal on paper, but you probably also don't want to use some free template you find online that may not be applicable to your state or your situation.You might consider just writing up a simple one page agreement that outlines the key points (purchase price, financing, inspection period and other contract contingencies, closing date, etc. and get it signed (and perhaps notarized for added formality?)

Old houses have cast iron pipers that will disintegrate (because of age and/or foundation shift).

Now if you have an old cast iron sewer with rust/scale lining the entire inside that’s a different story, plenty to get hung up on.  

I wouldn't think 3 feet of pipe would be a fix but it could be  however if you have cast iron you may  need to replace more pipe. 

I hear the wisdom in what you are saying...this is in both my and my neighbor's best interest to iron this out now.

When the first good comparable sold in my area I applied immediately, striking while the iron is hot. 

Ironically my neighbor in San Diego just leased his house out for $4,200/month.