Do i need a new collar on a toilet if i have a vinyl floor? never had one before
The ring can be 1/4" below the floor, although level with the floor is best. Modern wax rings (and some other newfangled sealing rings) are able to accomodate this. 

There may be some other reason the plumber is recommending repair or replacement of the closet ring. Armed with this knowledge, ask him/her to explain in detail why this is necessary. If you are unsatisfied with the response, thank the plumber and say you will call them back after you think about it. Then call some other reputable, licensed, insured plumber and get a second opinion.