I just want to buy a domain name with .blog TLD and it shows that this domain is "Tier 1 domain". Then I found elsewhere that these domains can't be listed afterward. Does that mean I can't put it in the marketplace to sell it for example? and why's that?
In short, a Tier is the type of rating that registry would place on domain name registration. Each tier specifies different requirements needed to own that particular domain name. A gTLD, for example will have specific requirements to own the specific version of the domain name, this can sometimes mean that the owner of the .com will have first "priority" of a domain name due to owning the business or residing in the country. The tiers will have a more loose requirement the higher the tier, meaning a tier 4 domain will have far less restrictions to own the domain name then a tier 1 domain name.
As far as "selling" those domain names, since there are restrictions on who can own them, someone who has the ability to purchase the domain name, can not then turn around and register that domain to someone who "Is not" qualified to own that domain.
Hope that is clear.