The methods that people use include: Broken link building Buying expired/expiring domains Guest posting PBN Buying/trading backlinks Profile backlinks Forum sigs Etc. Some, if not all, of these techniques could be considered spammy or questionable by the SEO community and/or Google. Currently, the first four on the list are considered to be worth anything (debatable). The others, don't even bother, other than for general traffic maybe.
This is the one to go for. I have had some success with broken link building. This only works if your content is good. If not they will just link to someone elses. I'm a big fan of editorial links where possible and I go for the guest posting and buying links (be careful with this as some sites are of very poor quality and are filled with lots of low quality links and this can have a negative effect too).
It's not all about getting many backlinks but getting backlinks (even few) from high page authority webpages. Blog commenting is also important even if it gives nofollow links.
The best forums for link building!! Although I have found that broken link building yield the best opportunities. Recently did a big broken link building campaign for a client. As wasn't as sucessful as I hoped, got a lot of replies, but several people wanted some sort of payment. I was lucky I had a budget but ended up costing a little more than I expected. I found it was mainly because more and more people are becoming more familiar with link building techniques.
Links worked, work and will work for no matter what industry you are in. Your competitors are doing that and it is just a matter who is doing it smarter. Unless you got a brilliantly new idea picked up by everyone in social media - but then it is not about SEO. You would not need to care
Aside from guest posting or exchanging links how does one generate HIGH QUALITY back links? emphasis on quality over quantity. For an eCommerce site like http://shopit.co.ke/
I think blogger outreach is the best method to acquire high-quality backlinks. Some good ideas are shared in this post: https://www.nohatdigital.com/blog/blogger-outreach/ I actually use some of those techniques and I know they work pretty well. I have acquired many high-quality links and built new relationships as well. In case you're wondering what program I use, I use https://mailshake.com. Easy to use and gets the jobs done. I highly recommend it. Here are some other tools as well: https://neilpatel.com/blog/10-blogger-outreach-tools-you-should-use-today/
There are other methods, such as broken-linkbuilding, expired domains, and such. Any backlinks should be within your niche and/or relevant to the content they are pointing to on your site.