It's easy to order from ebay, but I would only order from sellers that have very large amounts of feedback. Like, one seller in particular is pfootballpete4dhx, he's got a direct line to Pokemon and gets insane volume of product and usually has fair prices and sometimes can have some crazy deals. I've ordered from him a few times over the past year. Like, if you take a look at a shop and they have thousands of positive feedback with little to no negative and primarily deal in cards, then I would say you're good to go.

If you're opening modern product, the chances of what you open being resealed are slim as fuck. Most people only want to reseal high end product or packs, not random shit that you can find at Walmart any day of the week. Like, what you opened is going to be sitting on LCS and retail stores shelves for months without moving fast, it takes a lot of time and effort to do a reseal that actually looks semi legit. There's not a sane person on the planet who would bother wasting so much time for a cheap product, especially one that has nothing insane to pull out of it either. The only place I've ever seen people have issues with in regards to opening modern product is Amazon, and that's because they have a dumb return policy and let people return opened product and then try to sell it as new.