Plans, backup plans and being better prepared in general already does a lot to make them seem more professional.
The average ganger's good at threatening and might have some experience versus targets they know are easy prey, but if they're outmatched will scatter quickly.
The average corpsec in tonight's target building may be ready to deal with threats in general, but they don't usually have specialty gear and tactics ready. They know to shoot/tase lesser threats quickly and to find cover and call/wait for backup with heavier opposition, but they'll fail to react properly when faced with heavy opposition that's using (non-combat) spells, grenades or other things you don't expect from the common criminals.
But elites plan ahead and are prepared. They know how to best deal with specific threats and more often than not have the solution ready at hand. They'll have gasmasks on the second they spot a gas grenade, they'll recognize a spellcaster and have prepared tactics deal with it (geek the mage!), they know the layout of the place and have prepared sensors, traps and different strategies for dealing with assaults from any entry point. This makes them a problem if they're securing a place, but it's even worse if they're actively hunting you. You're dealing with people who (out)match your own skills, have vastly more resources to spend on legwork and they'll have done their homework when they choose to engage. They'll know how to pick the time and place and have that place prepared. Their magical backup will be tailored to deal with the spells your own mage uses most often. If your team has expert snipers, they'll engage in areas where long range is impossible. If your runner is a cross between Bruce Lee and Mohammed Ali, they'll do everything they can do deny him the possibility of getting in melee range.
Heck, you mess up bad enough and chances are that next time you just jump into the team's Bulldog, the thing explodes when the ignition starts and the 'runners that survived get picked off by snipers when they leave the wreckage... IF their safehouse doesn't just get hit by an incoming missile or artillery barrage. But unless they messed up real bad, it's probably better to give 'em a fighting chance.