We need new tires on 2000 Subaru Outback. Should I go to Costco for this? Or my local trusted car guy?
My SO and I just joined Costco and I haven’t needed tires yet, so I can’t give you a report on how well they do (and, of course, unless you drive to my store, your mileage may vary anyway). However, they tend to do other things well, in our experience, and we will probably buy tires from them when the time comes. At any rate, their customer service has a reputation for being excellent, so if they screw something up, they are very likely to take care of the problem.
As for 2vs4, you have an AWD car and need 4 new tires.
A Subaru usually needs the tire circumferences to match closely, so you probably need four new tires. This should be covered in your owner’s manual, so please read that section.
And start multiple threads.
I go to my local independent tire dealer for tires and alignment. I have gone to this dealer for years and would rather have the outstanding service I receive than save a few pennies.
I don’t belong to Cosco. However, the orchestra I sponsor just gave a dessert concert and one member of the orchestra got the desserts at Cosco. They were great! If Cosco’s tires are as good as their pies, maybe I would get a membership. On the other hand, the coffee in the waiting room at my independent tire dealer is awful.
" On the other hand, the coffee in the waiting room at my independent tire dealer is awful. "
That wasn’t coffee. That liquid was from the display that read,
" Does Your Transmission Fluid Look Like This ? Ask About Having It Changed, Today ! "
CSA
Its all about the wallet. What can your local trusted guy do for you pricewise, and if is prices are higher, is the higher price justified in your mind. For example, the local guy maybe providing all your car care at reasonable prices, he may be a lot closer to where you live and work so may be more convenient, other factors.
I have bought a lot of tires from Costco. They have procedures to follow, are well trained in those procedures and the procedures are all “best practices” that come from Michelin. But, they are not very flexible. They will not repair a tire if the repair falls outside the Michelin guidelines (three repairs max, at least 90° between adjacent repairs and not outside the belt area). If you want tires that are not in their “fit” guide, they will give you a hard time about buying them, but will cave in the end if you persist.
Costco tire techs are not trained in anything but proper mounting and balancing. If you have a mechanical issue or alignment issue, they are not likely to detect it or tell you about it. They don’t do alignments or brakes or any of the other services your independent may provide, so they have nothing else to sell. That can be good or bad depending on how you view it. They won’t sell you unneeded services, but they wont sell you needed ones either.
We have bought tires at Costco for the last 20 years and have had good and competent service. They also have free rotation and balancing for the life of the tires, in addition to the best prices in town.
BTW, about the 2 or 4 tire issue, buy a tire depth gauge and measure the tread depth of the two tires that you are considering saving. If the new tires have an 11/32" tread depth and the old ones have more than 9/32" then two is OK, other wise buy all four and periodically check the tread depth. when the difference between the deepest and shallowest tread depth is 2/32", then get the tires rotated, or rotate them on a mileage schedule. This is necessary for AWD.
Except for trailer tires I’ve been buying all my tires at the local Goodyear dealer for 30 years. They sell all the other brands too so can match needs and budget with their experience. I’ve priced Tire Rack and others and usually not $50 worth of difference so just not worth the hassle. Plus if you have a problem, you’ve got someone local to help.
I needed tires to last about a year five years ago and they sold me some no names. They were among the quietest and best snow traction tires I ever had for a couple hundred dollars. So I just deal locally. I also take the individual reviews at Tire Rack and others with a grain of salt. Seems like no matter which tire some hate them and others love them. The test results seem to be a little more reliable. I just rely on the local advice though. The last set I bought were Generals and they have been just fine over the last 5000 miles. One thing that is not readily available is what country and what plant the tires were made in. My Generals, Goodyears, and Michelins currently in use, plus my trailer tires were all made in the US, not Korea or China. Means something to me.
If Cosco's tires are as good as their pies, maybe I would get a membership.
The pies taste much better. 
In seriousness, Costco sells major brand tires like BFG and Michelin. So they’ll be just as good as any other store selling them. Their tire installers are probably happier and it would not be foolish to guess that they’re probably more experienced than workers at normal tire shops, because workers at Costco are paid well, treated well, and tend not to want to quit, ever - to the point where people who want to work there often have to wait for a new store to open up, because turnover is nil. I’d rather a happy, well-paid worker who’s been there a long time install my tires than have it done by some guy at a chain shop who’s paid in peanuts and hates his job and his employer.