Or if you have the phonw number just use a spoofing call app1. If you have Online details of the cc like bank access login you can check the balance online of the card
or you can use skype cand call the bank robot of the cc , they will ask for exemple UK cc's . with account number and dob , if i remember coreclty you can call the robor of the cc Bank , and the robot will tell you the balance of the card, this also works on Canadian cc's
2. cc sold by vendors are scams .don't buy from them nothing , specialy from thouse who say that the cc has 2k 3kask them .... how do they know ? (Show me proof)
cc sold by shops , don't contain full info , like bank login user;pass etc . but most of them have account number dob etc that you can use the call the bank robot and check the balance
3. ""I'm interested what is the difference and why they buy card they don't know if there is money on card or not.""
Itink they are buying thouse cc's for registering account like Ebay/PayPal/Gumtree etc or websites similar tothis , i have friends that do this.
4. Try to search and inform yourself what i told you in "1," i don't remember the phone numbers . every bank have their own phone number . to check the card if has balance or not