I think you should stick to your coding standards, but make sure you are up-front with your clients. Many clients do not know what it takes/costs to build good software. It's part of the professional developer's job to educate them.

Whether you're agile or waterfall, you get some sort of agreement from the client about what they expect the application to do. Too many developers (OK maybe more salespeople) are guilty of sandbagging. "They didn't say they wanted a highly secured website." In most cases, it's because they weren't asked. "Do you mind if your ecommerce site gets hacked?" Of course they care and why would you build it to let anyone penetrate the security? You have to educate them.

Just make sure you're doing only what the client is paying you to do. Part of your service is your experience. Clients expect you to know the pitfalls without them having to ask. It's up to them to include the requirement. You may want to pass on clients that want something cheap.