I agree with others - unless the discount was for older seed, I'd be unhappy too! Maybe they're trying to move some old stock?
I bought some garlic from The Garlic Farm a few years ago, and it failed miserably in my new raised bed. Upon contacting them, they admitted that one of their beds had been 'contaminated' and offered me a discount the next year. Needless to say, I didn't take them up on their offer and bought locally and have been saving bulbs for re-planting (while waiting for the bed to recover).
A few weeks ago, I bought some of my favourite Orange Paruche tomato seeds from fleabay, before I noticed that the chap sold mainly heritage seeds. Upon messaging him, it appears that these are 'F2' (saved seeds), which I can't risk growing due to only having a small garden (even if they do germinate, I could end up with anything or nothing)....
There are many seeds that will be fine (even well after their sow by dates), but I would be disappointed (and complain) too, especially if you were expecting good quality seed.
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