When i click on this link http://dispenser.tf/mall/trade/55479/ it gives me a "FILE NOT FOUND" WITH A STARFACE. So far its only this link. I have tried other listings and they work fine.
The listing is for a Backpack Expanders for 2.33 refined.

I had purchased about 5 of these yesterday but today i am unable to.

is there a limit to the amount of times you can buy an item? or maybe the seller blocked me if that is possible?

Nothing serious. I guess it was some kind of caching error that would fix itself.
Just remove the /mall in the link when that happens.

Like this: http://dispenser.tf/trade/55479/