This is easily determined by looking at the interest charge for any given month in amortization schedule.The reason you only pay “4-5% of all payments in interest” on your heloc that you paid off in a year is Because you paid the Whole Principal balance off.....this “ratio” nonsense is just more smoke and mirrors.To be clear, the monthly interest charges on a 30year mtg are calculated Exacyly the same as for a heloc.  

That was another thing I noted to them, as my place is "No Smoking".Are there cleaning services that specialize in getting rid of pet allergens?

What matters is that they don't smoke it inside a unit where there is a No Smoking clause in the lease. 

For instance, if every time you come, you say, "While I'm here, I'd like to check all the faucets and toilets and outlets again, just to be thorough... and I might as well also test the smoke detector battieries while I'm here...and can you turn on the stove for me to be sure it's heating, and all the burners, and are all the windows opening?????

is there any case where 'old' smoke/CO alarms are still 'grandfathered'?

I recently watched an episode of "Judge Judy" where the guest of the tenant was smoking a cigar on the balcony and somehow caused a fire.

Did you smoke something prior to this post?

I'm wondering if I should provide some sort of disclosure about the smoke detectors, water heater and renter's insurance?

Have you ever been evicted, have you filed bankruptcy, do you smoke, how much do you make, etc. 

Appreciate your advice and any expertise in this.Thanks If they both pass credit/criminal/eviction/landlord/income checks, and their combined income is enough, and they otherwise meet your criteria (no smoking, pets, etc.), you can't deny them.I'd really try to get previous landlords to let you know if he's had any behavior issues.