Most good slow drain will recommend replacing a gate valve regardless of its condition. The time to discover if it will work is not during a flood in your bathroom. If you have it replaced with a ball valve then check your water heater and laundry valves, too. Have them replaced at the same time with premium ball valves. Ball valve laundry bibbs make it easy to shut off the water to the washer after each use which may help to prevent floods in the future.
Examine the washer and replace it with a new one. Also replace screws in water line repair case they are old and damaged too. The new ones you buy should be durable and of good quality.
After you have the stems out you should be able to find the washer on the "inside" end. If it is nicked, torn or brittle it is likely the cause of your drip. Even if it looks brand new, go ahead and replace it. You've already come this far. You can get replacement washers at almost any hardware store. Sometimes you may want to replace the whole stem, especially if the handle end is stripped out. It's best to just take the stem with you to the store and see if you can match it up. Most Do It Yourself stores have replacement stems for many popular brands. If your valve has a center diverter valve to switch the waterfrom the tub spout to the shower head the same process applies. Many times it is easier to replace the diverter stem than to repair it. This really depends on the design of the stem.
10) Tighten down the closet bolts making sure NOT to use too much torque. You aren't installing tires on a race car here so, take it easy Mr. Goodwrench. You just want to hold the toilet in place, not crack the porcelain base of the toilet or damage the drain flange.
Investigate the plumber's reputation. Ask a neighbor before starting your search or check online for customer reviews. Call the Better Business Bureau or your city to ask about any complaints on file against this company. Finally, ask the plumbing company for references from customers. If they are reluctant to provide references water line repair call another plumber.
And the way to know what's sufficient? Well, until the work is done an the bill paid you won't know for certain, but this is the best that can be suggested and normally works very well.
By the time that you have made your pick, make sure to check ID and Certification. Remember, these individuals will be doing their works inside your home. The security of your family is also an issue here. If they can't present any papers of identification, then don't take them in! When it comes to your family's safety, there's no room for experiments.