How to know whether or not it's LTE on 2100 and 2600 MHz. Unlocked Z30 purchase.

Question

I'm eager to know if the Z30 is good with the 2100 and 2600MHz bands.
LTE-good.
I read Crackberry.com discussion threads. 
It seems that some phones (versions) don't do LTE on some bands.
E.g. Z30 version STA100-5 -- band 17 -- isn't LTE.
This can be important when you move from one carrier to another,
or when you buy a phone independently of a carrier.
I found vendors of unlocked Z30 (hope this is OK to post here).
First: please point me to the terms to search on, or let me know
which things to look for, when purchasing a Z30 independently of a "carrier". 
Here's why. My carrier is Fido:
Your device must be compatible with the Fido network, which uses GSM, UMTS, HSPA and HSPA+ at 850 MHz and 1900 MHz and LTE at 2100 MHz and 2600 MHz. 
If you are unsure of how to check the frequencies your device supports, try the manufacturer's official website and search for the specifications for your particular phone/smartphone model;
I can get a locked Z30 from Telus and then unlock it. 
I can get unlocked Z30 phones from individuals who have some supply
but I want to know what smart questions to ask them instead of just buying
it simply. When buying from an individual, there may be no possibility of return.
I'll share more, when I get answers to my question about the 2100 and 2600 MHz frequencies

Answer 1

1. How can I make sure this phone that I would like to buy (880$) is indeed Factory unlocked?
Purchase only from an official source that sells officially unlocked phones. Otherwise, you run the real risk of purchasing a "hacked" phone.
2. What is the disadvantage of getting one unofficially unlocked,
Lets see here...every time you update software or restore the phone, it will re-lock to the carrier it was originally locked to...some things(hard to predict which ones) may not work properly from time-to-time...etc., etc.