Depends, where I live right now doesn't process packages that great so there's a huge incentive to buy in-person, whereas I used to live in a rural area and availability dictated buying online while timeliness dictated buying whatever I could get in-person. If I have to take a 50 minute trip for it back and forth to get it in-person, I'd probably rather wait a business day's shipping (excluding weekends) unless I have nothing to do and feel like going out.
I buy clothes online as much as I do in-person, but only from stores with long return windows or where I trust the fit from having worn/tried stuff from there before. Shoes it depends very much on you, for me I won't do it anymore despite no negative experiences because of all the problems I've had in brick-and-mortar shoe shops with shoes in my size not walking comfortably (half-sizes rule). Online buying is also a nice aide to brick-and-mortar in that you can try a thing and then, if you need a size up or down or different colour w/e, you can just order it online. Not to mention price matching (this is a huge one with electronics, if a fantastic way to irritate people in electronics stores). If I'm making a majorly expensive electronics purchase odds are I'll buy it in person though, unless it's computer parts or something. Skincare stores are best used to examine the product for the first time then just order it online if you want more... (perfume too)
Books have really annoying shipping prices, so I only buy online if I can't get it elsewhere. I have too many books to read anyway. Books are an example of something that's fantastic to brick and mortar shop, though, especially used bookstores, but of course as I say that a lot of bookstores are shutting down due to digital book technology (which I also make lots of use of). While on the subject, libraries are also better in-person with regard to service/browsing opportunities/environmental ambience/not having to ship the books back and forth, although as they increasingly digitise their collections there's less incentive...
It's good to be able to physically examine produce. I've never majorly food shopped online (read: I've bought candy before) but the main problem there is a) I've never really lived in an area where it was an option before b) now I do, the place I live makes delivery unviable. Travel-related stuff always online because $$, though I've heard some people like to go to familiar brick-and-mortar reps and price match. That's pretty much it, gaming-related stuff is a mix and match based on the item.
As for e-stores: I trust because of word of mouth combined with researching online (for secondary word-of-mouth and any articles about insolvency, scams, etc. that might be relevant). I buy from user-storefront sites like etsy/ebay (rarely)/amazon too, I'll have a look to see if there's negative feedback and how much positive feedback there is but I think after buying online for many years, instinct + knowledge about the product (e.g. if you're ordering figurines, know where the bootlegs come from, know their hallmarks, etc... also some stores are better with some products/departments than others) + fact-checking makes most sellers come out actually pretty reliable as far as people who want your money go... Amount of information about stuff like shipping policies, payment policies, packaging policies helps. Most of the time you can buy from the same places repeatedly anyway.
I try to avoid ordering internationally unless I can get a tracking number, but I've been doing it for a long time and only had something get damaged once, don't think I've ever even had something missing. [note: the main thing to be wary of with most sellers is not getting scammed, it's their security with your personal details, IMO]
Would never order online: meat, my meds (well, this one depends on the future of pharmacists... I try to cultivate a good relationship with my pharmacist too which is useful because I need advice a lot), something I can't afford to get lost in the mail or damaged by customs, makeup/perfume I hadn't had a look at first
