Internal Revenue Code Section 1031.

I can't imagine changing codes every guest.  

I am curious though: if you locate a good property, and by good I mean (as an example)  3br 2 ba SFH, in a hot zip code, with plenty of comps to figure ARV, at 70% of ARV minus well estimated repair costs and reasonable assignment fee, and then offer it as is to investors in current market, how difficult would it be to sell it if your trusted/connected buyers didn't want to buy it?

I believe that under a standard title insurance policy, building code matters, zoning and other governmental restriction on the use of the property are excluded from coverage so unless you purchased an extended form title policy there probably is no coverage, but it never hurts to submit a claim. 

I was considering getting just SIP panels from china, and reputed SIP panel companies in china says they do not ship electricals and plumbing as local codes monitor them closely.

It just makes the HO responsible for all work done to meet code. 

Since you’ve offered the $300.00, honor it.Notify them that moving forward you will not be able to provide any further rent credits and offer to break the lease if they feel the living arrangements are no longer working for them.If you feel the above is something you are not comfortable with, I wish you the best of luck with tenants that’s will drain you while they occupy your premises. 

Think of the IRS code as a behavior incentivizer.  

These are professionals with additional training and a stricter code of ethics.

Just be honest in your ad and honor what you say.3.