These are just my opinions, so it's understandable if you disagree, but Rankpop's business practices are much different from mine and many other SEO companies I correspond with.
I see you said initial $450. Does this imply there are future payments? Their website makes it seem like it's a one-time $450.
Anyway, 10 keywords for $450 would blow most SEO's minds. You add up 10 small keywords and it becomes a relatively big task. MAYBE 3 low competition keywords for $450 per MONTH but not 10 one-time (unless they also do monthlies).
It's just that the time needed for 10 keywords, if they do it right, effectively puts them around minimum wage, and I could go work at a retail store for way less work and the same pay if I was going to pay myself near minimum.
The reason they won't let you do "coffee cups" is because it's too competitive for their flat rate scheme. However, a good SEO knows that if a customer wants a keyword, then they will get that keyword. Granted, any other SEO will likely charge you well over $1k for "coffee cups" and 10 related keywords, but they wouldn't tell you flat out "no."
"Coffee cups" has 5k exact/246k global searches and the first page sites all have decent authority. That's why they don't want to do it. Maybe it's too hard for them, or maybe they just don't want to change their price structure, but the point is that they told you no when you deserve a yes because it's your site.