If the age of your equipment is older, or it stops functioning, those repairs can also add up.

I bought 1 House out right, I am refinancing for 100k. had 1 renter paying 1000. using the refinance to purchase the second property, and putting renter for 1400. it will also need 25k in repairs.

I just listed my last property for sale, a fourplex in Pocatello, because now I focus more on commercial RE and syndications to be a true passive investor and not deal with tenants and repairs.

Repairs: Add a pool ($65K).

Quote from @Dan Grove: Some combination of cash to seller, closing costs, repairs, construction, paying off arrears, assignment fees, commissions.   

Assume a couple of months of vacancy, consider potential unexpected repairs (like HVAC or plumbing issues), and test the numbers with rents dropping by 10-15%.

(Foundation, etc)4) Black mold, asbestos, lead paint, other other costly repairs. 5) It need significant cosmetic repairs where the purchase price just isn't worth it. 6) They may have an odd layout of the rooms. 7) Non-compliant septic.8) Trouble with permits or tenants9) Listing agent has a poor or incorrect listing.

Could I instead hire foundation repair and soil stabilization services to prevent foundation issues?

With my own portfolio I generally underwrite with 10% for repairs, 10% for cap ex, 5 percent for vacancy. 

That aside, If it were me I'd get a professional estimate of what repairs would cost, and make the decision to keep or sell based on that.