There are many situations in which u can get black listed, some are time bounded while others are for ever, some of them are as follow:
1) U resign from a company and get ur resident permit cancelled b4 its actual expiry-u get black listed or u can say face a ban for 2 years only.
2) but if u abscond i.e for eg u go on leaves and does not come back and if the company reports this to the immigrations then u must say bye bye to qatar u cannot enter in to qatar.
3) any crime resulting in ur deportation also means forever.
There are many situations in which u can get black listed, some are time bounded while others are for ever, some of them are as follow:
1) U resign from a company and get ur resident permit cancelled b4 its actual expiry-u get black listed or u can say face a ban for 2 years only.
2) but if u abscond i.e for eg u go on leaves and does not come back and if the company reports this to the immigrations then u must say bye bye to qatar u cannot enter in to qatar.
3) any crime resulting in ur deportation also means forever.
i think this will help u.