Depends on what kind of stamps they are and from which countries.
But I know for 99% the answer to your question is NO.
He will probably tell you your surplus stamps are worthless junk (he will really use these words!) and are a waste of his time. He offers maybe $10 if you are lucky and if he can sell the lot on Stampboards as a "Junque lot" for $50.
IMPORTANT piece of advise: DO NOT send your surplus stamps to him without contacting him first. He will NOT send them back if he is not interested or only if you pay the postage costs.

Do not trust this guy as far as you can throw him. He's dishonest and arrogant, and can be abusive. You'd be better selling the stamps on eBay, though that would take some more time and effort. Glen is one of the most unpleasant individuals I have ever encountered, so I would suggest you find an alternative.

I totally agree. Told me my speciman stamps were illegal and brought in one lot. Took me around 20 years to assemble. Low ball price. Told him to send them back to me. Don't deal with this guy. Thinks everyone else is a crook

No, he can't be trusted, read other comments posted by people here that he has dealt with. You will get screwed in one way, shape or form. He's only concerned about himself, and no one else.

Sold off a few countries i no longer collect. Mailed them registered and got paid by paypal in 3 days. And price a bit more than I expected - he took it all no cherry picking which my local dealer tired on me