One thing I've learned in this industry over the years is landscaping is extremely subjective. ClIents often tell me "I'm taking bids from a few vendors." This is where landscape design and construction are very different from an electrician coming to install some light fixtures or a plumber coming to re-pipe your home. With those trades the factors are quantifiable and easily compared. For example, an electrician will be using the same materials and most likely very comparable products. An experienced plumber will know how may feet of pvc he'll need, and how long it will take him to do the job. With landscaping, because there are so many other variables like overall design, plant size, plant cost, plant spacing, and most importantly the quality of the prep work, bids can vary greatly. For a larger scale project this is my advice - Get an architect.
A licensed architect can take the guesswork out and see to it that your contractor follows the scope. Contractor "A" may have given you a lower price, but did he include the excavation of existing soil and the addition of 4" of composted mixed soil in his bid like contractor "B" did as the plan specified? Probably not. Accountability and comparability are factors of why spending the extra money for a working plan will pay off in the long run. A healthy landscape involves much more than buying plants at a nursery in slapping them in the ground. The preparation work is what separates most professional landscape contractors from the guys and gals that are just winging it. Do your research and ask lots of questions to make sure your contractor has done his or her homework. Trust me. It'll pay off.
If it's a smaller project, spend your time vetting your potential landscape contractor in order to qualify them. Angies list, nextdoor.com, BBB, and Facebook are good places to start. Once that's done, give them a realistic budget as a framework to work within. Trust that they will give you the most value for your hard earned money. Remember - good work usually isn't cheap and cheap work usually isn't very good. Best of luck and don't forget, you can contact us for help. :)