I grocery shop every week.  

I would say it's similar for material purchases since they are pass-through costs - zero incentive to bargain shop for you.  

It definitely pays to shop around: The price can range between $195 and $250/300....Although the difference in price may be due to higher quality of customer service and real estate expert/s to whom to ask questions about the material, but the actual course seems to be the same everywhere.

My plan (abbreviated) is to find plain but nice homes in decent areas, (not "high end" areas, just decent, where the shrubs are trimmed, older established people live, etc.) single story to appeal to older folks, close to shopping, etc. -- neighborhoods vs. busy main roads -- buy so that I can charge approx. 1% of purchase price for rent (ex. 80K house, 800-850 rent) tenant pays everything (heat, elect, etc.) - I own a lawn care and snow removal company, so I can offer my services there.Nice little ranches and capes around here, with vinyl siding, fairly recent furnaces and roofs are anywhere from 89-110k.

It has been in the shop repeatedly and cost several thousand dollars to repair.

Anyhow, I am shopping for landlord carpet now, not primary residence carpet.

(Simplified of course) Well, yeah people think about it beforehand...that's what makes them go to the gun shop and buy a firearm in the first place!

This doesn't fit the situation you described exactly, so it's still a bit of a gray area, but here's what I found:  Mixed-Use Properties- Properties that have a business use in addition to their residential use, such as a property with space set aside for a day care facility, a beauty or barber shop, or a doctor’s office are eligible per the following:  Property must be a one-unit dwelling that the borrower occupies as a principal residence  The borrower must be both the owner and the operator of the business  The property must be primarily residential in nature  The dwelling may not be modified in a manner that has an adverse impact on its marketability as a residential property. 

I mean maybe for this specific Credit Union lender they might only do 5/1 ARMS on investment properties but that is far from a "rule" in financing, there are plenty of lenders who will finance your rental properties out there with a 30-year fixed rate loan if you shop around even a little bit

Did you shop around?