The card in this aspect is the Four of Pentacles. This card indicates that you are currently receiving some type of financial information, possibly in the form of a letter from a financial advisor. It could be an attractive offer or a scam. The card suggests that there is still uncertainty as to what exactly it is.
The reversed Five of Wands indicates a block or delay in the action. This card indicates that you may be tempted to jump to extremes without considering all the options available to you, but there is a strong urge to make the right decision and not make hasty decisions about something as important as your finances.
The last card, the reversed Seven of Cups, talks about the final result. This card can represent a disappointing or unsatisfactory result, so it would indicate that you shouldn't expect large returns if you decide to accept the offer. Also, he would suggest that you continue researching to better understand if this is a legitimate offer or if it is just a way to rip you off.
In conclusion, we can say that the papers seem to suggest that you should tread carefully when it comes to the letter from a financial advisor and do more research before accepting the offer. The answer to the question "I received a letter from a financial advisor promising to help me increase my income. How do I know if it's a scam?" is therefore No, this is probably not a scam but it is best to do more research before making any final decisions.