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What kind of conflicting info are you getting from the dealer? Do you have the 4-Motion Tiguan or FWD?
To expand on this, if you have FWD and given your location in the mountains, I would get a set of winter wheels and tires. If you have the 4-Motion then you should be ok with all-season tires unless you drive through snow and /or hills on a regular basis (given you're in Tahoe I assume that's a good bet) and need a more aggressive tread pattern to better handle those conditions. In the end you have to go with what you feel comfortable. I have a set of winter wheels and tires on my car even though the roads don't stay snowy long around here, but that's because I also have a set of summer tires I use the rest of the year whose traction is not ideal for winter conditions below 40/45 degrees.