The applicant lied about having no prior evictions.

Natural Gas is also the newer technology compared to a boiler and hence will age better when you go to sell the property whenever that will be.

Assuming the prior owner wasn't lying, it does sound like you may have a leak. 

I would discuss all the possibilities with an attorney and see where your comfort level lies, after that discussion. 

:) :) Smiley faces to show I'm not trying to be obnoxious but yes I am yelling, in a hopefully friendly way.The answer you are seeking lies with your target market, not with agents.

Should they try to flip houses from out of the country using all of the technology available nowadays?

Shame on the agent who advised you otherwise and basically suggested to lie/commit a crime because “who would know?”

Your renter is giving you two red flags - no rental history (which may be a lie and he has been evicted before and doesn't want to tell you), and bad credit, which means he's cheated someone else out of money. 

In my state, the Seller must provide written proof of receipt to show it was received by the Seller.Either your agent is lying to you, your agent is failing to properly contact the seller's agent, or the seller's agent is specifically ignoring your agent.If you believe your agent is doing everything right, have them contact the seller's broker and explain what's happening.

Even as a web developer, and avid technologist, I don't believe technology solves everything.