how long have you been actively selling for?

Usually its around 90 days of sales history before they will grant the buy box,

It could also be as simple, as your price is too high.

I’m getting the impression that you all think this is an acceptable way to conduct business.

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Also Feedback , speed of delivery and customer service seems to be in the buy box awards too .
For example .I found that on one item I sell at £7.43 is 7p more expensive than another seller .
I am at currently on 100% feedback in the 90 day period wheras they are on 84% and I deliver items quicker and keep my nose clean ,so the system awards me the buy box over them for the item although it is more expensive ,So it proves in my case on several items, you dont have to be the cheapest to get the Buy box!
Having the buy box also doesn’t mean that you will get the order from Customer they also tend not to purchase from a Quality Seller , check your Postage settings.

Ok, so 90days seems to be the key here. That was not mentioned in my many contacts with Seller Support.
Amazon suggests that the main requirement for a BB is that you are a Professional Seller …and do all the things that are normally accepted for a USP.

There are many buy box examples in the Books category which defy any sort of logic and appear to flout the very limited amount of “rules” that Amazon tell us about… There are numerous examples of vastly overpriced books with sellers with very poor feedback getting the buy box. I assume this happens in other categories.
I surmise from this that the “rule” that Amazon are keeping from us is:-
“We reserve the right to give the buybox to anyone we like regardless of how unfair it is to everyone else”

There are Many things AMZ do that Make many sellers life difficult, and sometimes policy’s or decisions made are just straight up counterproductive to a fair and competitive capitalist marketplace. However, in my relatively limited experience on the platform, and so humble opinion, the Buy Box does not fall under this category. As some sellers have mentioned, if your account is under 90 days active, and you are not listing under FBA, You are almost certain not to be given Buy Box, why? Because AMZ does not want to promote an offering from one whom they have no data from regarding performance, they are protecting the buyer, and actually you also, lets say you have 500 units, Buy Box is given, you make a serious amount of sales, but you cannot fulfill all orders effectively due to lack of experience or unenforceable issues, you will have issues with orders, cancellations, late delivery etc, and then your problems will be much bigger than no buy box, in this situation you may have no account! Frustrating as it may be, AMZ platform is not the place for quick turn around’s with regards to cash flow. My Advice…

Wait until account has been on for 90 Days
Dont stress yourself with communication AMZ support, they wont help, and you will feel extremely frustrated.
Continually lower your price over the period of an hour, and then check when the buy box is live, then you will know price point for AMZ’s formula of accepting Buy Box.

And finally dont stress over it, Being new on this platform is a struggle, and nothing happens quickly, keep plugging away, make the right decisions, be productive, dont give up, expect many more disappointments and set backs.