Do a Pricescope search. You did not give any cut parameters or tell us if a lab graded the diamond, but using what you told us, I searched Pricescope and came up with 35 listings between $3500 to $5000. So, while this diamond might be okay for the money, there are many listed here as G-SI1 for less, and none for more.
Mistakenly listed the color as "G". It has a "F" color...
It was GIA graded:
Color: F
Clarity: SI1
Polish: Excellent
Symmetry: Very Good
Depth: 62.3%
Table: 59%
Oval 1.07 carat
$5500
I did a Pricescope search. Just looking for an area to compare this price to. I've been acquainted with this jeweler for years, and he claims the diamond would go for $3k/$4k more in a "wealthier" area...& insists that I'm getting a deal. Searching for something to counter with.