I don't think it will lower trust, rather it won't let your long time pages increase it further.
It's not a problem, but you're cutting yourself off of a gain... in my opinion.
What i don't get is that... are you the maker of these products?
Or are you just selling them ( perhaps even as affiliates )?
Okay, IF you're the manufacturer, or perhaps a long time and trusted seller, here's what i'd do... ;)
I'd keep the pages, only have them linked to in a different link hierarchy, ie. not the product index, but something like the "product archives" or "product history" or whatever. Keeping the URLs the same, but of course adding something like "we no longer carry this product" to the page, removing links to payment or perhaps even say "We don't have this anymore but maybe you'd be interested in this"... i mean if you have similar things... why would it hurt to tell people about it. ( Sorry there's just way too little info on what you do on that site :P )
IF it was unique that is.
If it can be found just about anywhere on the net, then this isn't a good idea. Make that... don't do it then.
But in case it was unique, or offered some unique information, comparison, whatnot... i'd say keeping it under such a category would not harm you. If their PR would drop because of the new category, they'd become supplemental at most. They'd still be there, and showing valuable historic data both to visitors, and google ( about your site ). The history of URLs does play a role in trust i think...
( must have read it somewhere :P )
So if it wasn't just an affiliate feed, but unique info people might still find interesting... i'd say keep it, just in a user friendly way. And add a vote button, or counter to see if enough people are curious about such products for the company to carry them once again :)
If it can be found elsewhere or has no additional value other than the "buy now button" delete it NOW >:)
Gah... i keep envisioning a normal business with a website. My fantasies are blurring my vision... ( gotta keep remembering this is a webmaster forum... people here rarely are the manufacturers themselves )