Re: post #1. The way you’ve written it, bona fide means the equivalent of ‘genuine’:
… to genuine customers like you.
If you want it to mean ‘good will/good faith’, then it needs to refer to the offer, rather than the customer:
‘To maintain your custom, we will offer you an additional bona fide rate of 5%.’
Re: post #2. You’ll notice that I changed the phrase in my example above because ‘customs’ was incorrect.
(custom = Regular dealings with a shop or business by customers)
Re: post #3 There’s no significant difference in meaning.
Re: post #4 Yes. Use one or the other, but not both.
Why have you deleted some of your posts? Now part of the response doesn’t make sense.
I only said what it related to - I never said I would use it that way. In fact, I wouldn’t use the phrase the way you wrote it at all, which is why I indicated ‘bona fide’ should relate to the rate.
‘Loyal’, rather than ‘genuine’ would probably be the correct term in your example.
'To maintain your custom, we will offer an additional bona fide rate of 5% to loyal wholesalers like you.
The phrase ‘genuine customers’ is in common use, but refers to customers who fully intend to make a purchase, rather than those just browsing or picking up free giveaway items, etc. with no intention of purchasing goods or services.