In case you're interested, here was the arena's reply:
Thank you for writing Guest Services!
"Standing Room Only" is located on the 400 level, which is the highest guest seating level at the AmericanAirlines Arena. A Standing platform is located on both the East and West side of the Arena, but depending on the event, one or both sides may be closed to the public.
Should you choose to purchase a "Standing Room Only" ticket, you, as well as other ticketed "Standing Room" guests will be standing throughout the length of the event, as seats are not provided.
In regards to "buying some tickets from an agency": Please be advised, that the AmericanAirlines Arena has authorized TicketMaster to sell tickets for the event, and the purchase of tickets outside of TicketMaster or the Arena Ticket Office is not advised.
Best Wishes!
Guest Services