As an experienced gig buyer, I can tell you that a lot depends on how you do it.
Here's how I make sure to get awesome results from my purchases:
Step 1: Define the task you are looking to get accomplished.
Make sure you know exactly what needs to be done.
Good: I need to transcribe a video
Bad: I have no idea how to rank on Google so I will browse Fiverr for gigs that promise first page rankings
Step 2: Define what is important to you
Good: Accuracy is crucial (specific)
Bad: I want someone good (too general)
Step 3: Use Fiverr search to look for what you need
Step 4: Sort results by rating
Step 5: Look at gigs with 100% rating that deliver within your time-frame
Step 6: For each gig, read the description, look at samples, and check out reviews. If relevant, make sure the samples suit your preferences. Ignore generic reviews, and pay attention to what's important to you (from step 2).
When you are done, you will probably be left with a handful of possible gigs.
Step 7: At this point all the gigs you are left with are good. Go with your gut feeling or pick the one with the most reviews.
Step 8: Order the gig
Step 9: Don't expect perfect results. Remember - you paid $5 for this. Don't expect a $500 job.
Step 10: If the provider did an excellent job, keep their name on file so you can use them over and over again and skip steps 2-9 in the future :-)
Examples of what I like to get on Fiverr:
* Graphics (ecovers, logos, facebook covers, etc)
* Video creation (not fake testimonials - those are unethical)
* Sound and technical editing for videos (a Fiverr provider once saved me by fixing a bad launch video)
* Writing (keep in mind that most writers will not be great quality)
* Submissions (article directories, bookmarking, video submissions, etc)
* Technical problems with blogs and other sites
* Little programming jobs
Do it wrong and you'll waste your money. Do it right and you'll get great work done for a tiny cost!
I hope this helps someone. If you've got anything to add or a question - post it below!