Will this combo work?

I'm looking at new set of wheels and tires. The wheels are 18x9 Worx Beast and the tires are Toyo Open Country MT (275/65/18) The sales person tells me that i need to have a -12 offset. I currently do not have a lift and may have plans to have one installed later. I have seen posts the show guys running this size tire with out a lift.It does require some trimming and I am ok with that. Question is, is the sales person correct? I have never bought new wheels and tire so I'm unsure of what will work. Also any advise or if you know of things i should look out for would be helpful.

Truck
2012 TRD Sport DC

 

Would be best to try it on before you purchase. What are the wheel specs of the new wheels? Back space and offset do play a roll in fitment, especially keeping the tire off of the UCA when going with a wider/ taller than stock tire.

 

The wheel specs are the question. Currently don't have a lift or leveling kit and not sure if i have the cash to install or now. They are telling me if i don't have a lift i need a +12 offset. If i do have a 3" lift in need a -12 offset. I do know that the +12 will not work with a lift installed. But will the -12 work on stock for now. I think it just might stick out from the fender a little. Is that correct? So should I go with the -12, that way if i want to lift the truck in the future i have options.