Yes, Dolphin is 100% customisable. As others noted, it's a LAMP open-source platform, which happens to be the most popular stack among developers worldwide, making it easy to find help.
Boonex team does not offer customisation service for Dolphin at all. Plenty of developers at Boonex Market and elsewhere that do. They are all independent. We don't take commissions and we don't have any means of control over them. All we can do is make sure that those registered at Boonex Market are observing the community rules. If they don't, we can suspend their account. That's all the leverage we have.
Regardless of which platform you use, Dolphin or any other, if you seek external help you may end up with a really bad or a really good result. Research, ask around and assess work frequently before investing any money. Even when you find someone, pay only in small iterations, for bite-sized results that work.
Now, I have to say that this is a common, very very very serious, pressing issue. A lot of webmasters get trapped in endless loops of customisation rounds with little to no marketable results. We may not be directly liable for that, but we do sympathise and want to address this issue. Webmasters often have confused expectations about what can be customised and what implications the changes may bring. If you stick to "stock" setup and only customise via admin settings, you would have no problems with updates and any technical issues can be rightfully addressed to the platform developer. If you modify core modules, however, expect an ever-increasing flow of compatibility issues. If the mod is absolutely critical for your idea, you need to find the right people that would not only implement it but would support this implementation for years to come. Even the smallest custom changes have serious long-term consequences. We know it all too well, and that's why we make all those "builders" that allow customisation without modification. In UNA, for example, we have taken it to an extreme, painstakingly isolating every modification into own "app", which can be activated/deactivated without disruption to the rest of the site. Our plan is to not support/promote any non-modular modifications in UNA at all. If someone needs something special in UNA, they would have to get us or someone else to develop "tailored apps", which cost a lot more than the platform itself and have to be maintained/paid-for through ongoing monthly service subscriptions. Tailored apps are for webmasters with bigger budgets. It's something in between of using stock software and hiring own full-time development/engineering team.
One of the reasons why we renamed Dolphin into Dolphin Pro is that the site operator needs to be somewhat of a professional. Not necessarily in coding, but at least in operating a CMS-driven website... finding the right people to help, trying settings, asking in forums, etc. Boonex community is relatively anarchic and open. You have to navigate dangers to find gems.
UNA, on the other hand, offers more customisation potential via Studio and extensions marketplace is tightly controlled. It's a "just works" platform for non-technical people. If your ideas go beyond Studio capabilities, prepare to pay around $1600/month or risk getting in big trouble.