I think it depends on where you are looking. I've used Orlando Ticket Deals or Attraction Tickets Direct before and I've had good service.
I wouldn't buy anything that "seems to good to be true" and I wouldn't by from Ebay. If you have a company you are thinking about, let us know and one of us may have used them in the past
My rule of thumb is if you have to question it then go with the safer choice.
WDW = 39 visits since 1979
DCL = 3 cruises since 2002
[COLOR=rgb(255, 0, 0)]Dec 2014 [/COLOR]= WDW - Animal Kingdom Lodge - Grand Villa Savanna View
[COLOR=rgb(255, 0, 0)]Feb 2015[COLOR=rgb(0, 0, 0)] = DCL - 5 Night Western Caribbean on the Wonder - 20th Wedding Anniversary Celebration[/COLOR][/COLOR]
[COLOR=rgb(255, 0, 0)][COLOR=rgb(0, 0, 0)][COLOR=rgb(255, 0, 0)]April 2015[/COLOR] = WDW - Boardwalk Villas[/COLOR][/COLOR]
Have only ever bought online and never had a problem.
As long as you are using a reputable company and pay by credit card as this gives you exta cover just in case.
I have used Undercovertourist, Florida Tix and Travel Republic and many others that I can't remember.
UK people can get much better prices than US as the companies buy in bulk there's no need to pay Disney prices - they are usually more expensive