Honestly? Nobody can truly guarantee that, and anyone who does should be approached with caution.
There are two ways to appear at the top of Google. The first is Google Ads, which is the paid route. You set a budget, and every time someone clicks your ad, you pay a small fee. The more competitive your industry, the more each click costs. If your budget is healthy enough, yes, you can be at the top of Google tomorrow. We offer Google Ads management as one of our services (with over 15 years' experience at keeping spend efficient). Set up properly, it can be a brilliant tool.
The second way is organic, where Google ranks you naturally because it trusts your website. This takes longer, but it does not cost you per click, and the results build over time.
Now, the warning. You will come across agencies and providers promising guaranteed organic rankings. The way they do it is by generating hundreds, sometimes thousands of pages on your website using AI, each one a slight variation of a service or location (think "plumber Bolton", "plumber Salford", "plumber Bury" and so on, but at scale). It works for a while. Then Google catches up, recognises the pattern as low-quality, and penalises the site (do a search for 'scaled content abuse' to learn more). We have seen a similar thing in the past with keyword stuffing in the 90s and link farming in the 2000s. It never ends well.
What we do is the slower, sturdier route. We help you build something Google can actually trust over time, hand-built pages with completely unique content, so your rankings grow with your business and cannot be wiped out by an algorithm update. It takes longer, but it lasts.