With some cheap limousine services, you have to make sure that they deliver the quality of service you really wanted for the occasion. It is not uncommon to have poor services from cheaper limousine companies. Poor service might include badly maintained vehicles, shoddy upholstery and an unfriendly chauffeur and staff. There's also the question of reliability. If the limousine has any problems (a flat tire, or overheating) there might not be a backup. These are not merely inconveniences or nuisances, but a failure to deliver. It would be specially embarrassing when there's an event or occasion which depends on promptness, like a wedding for instance.
Although most of these could be avoided with a clear agreement on expectations, it does happen sometimes that you'd get older model limousines rather than the one you specifically requested. Or worse, a vehicle which wasn't cleaned in between jobs. Finding stale wine in an ice bucket of water is not funny when you're on your way to a funeral.