As Bruce said, gas lines are not that hard to repair, not more different that plumbing but if the issue is buried behind drywall the cost goes up some.I'd rather negotiate the price down and do the repair my self, that way I know corners were not cut. 

Don’t go cheap, don’t cut corners.

The natural reaction is to significantly cut your rate to attract business.

Also note since you are going through agents you will want to make sure they get their cuts as well. 

Cut your timeline in half and aim for three months.

You right, I bought property with “all cash”, and I do intend to refinance the property but there are no tenants in the house yet so I guess it’ll take some time until I’ll be able to refinance, unless there is a short cut I don’t know about.

Joists which have been "notched" or completely cut to accommodate some "update" can create severe structural issues causing leaning floors and tight doors.Others have already mentioned asbestos/lead based paint issues, however you rarely see remediation costs mentioned...they can be VERY high, and the fines for violating Fed/Local EPA laws can start at $11,000 for a first violation.

I see way too many people hear about 1 group and get so laser focused on that one team, even when there are 100s or 1000s of deals out there to consider.   

This will cut your living expenses dramatically and you'll be building equity with an appreciating property. 

You get in the game of property ownership at the expense of being house poorer, which would cut down your savings rate from where it is now.