This is the nature of all disputes. However, courts favor evidence over simple words. Courts are also aware of the fact that defendants will lie and try to make their actions seem justifiable.
For example, if your work was indeed substandard, why didn't the customer communicate this fact to you before a lien was recorded? If the defendant claims they did not pay because the work was of poor quality, it seems reasonable they would have mentioned this before it became a legal dispute. The court will likely find the defendant's defense theory somewhat suspicious.
It should never be "their word against yours", was the job inspected? Did the city inspector find the work acceptable? Who is a better judge of a quality installation, the city inspector or the customer? Was there a written contract itemizing the scope of work and was that scope of work completed?
If you have satisfied your contractural obligations, it is time for the customer to satisfy their's. If you have your ducks in a row and have maintained your end of the bargain, you should not worry about what your customer might possibly do if you exercise your legal rights.