Biblatex: Inconsistent name-format

Change your first entry to remove the extra set of braces in the author:

@book{medianmean,
    author={Agresti, A. and Finlay, B.},
    title={Statistical Methods for the Social Sciences},
    publisher={Prentice Hall},
    edition={3},
    year={1997}
}

By having this extra set of braces, you are telling biblatex that the whole line is effectively one last name, and it prevents things from breaking up semantically the way it is intended.

Remember that whenever you want to tell biblatex (or bibtex) that something should be kept just the way you write it, you can wrap it in another set of braces. This keeps a title like "The creation of the {I}nternet" with the proper capitalization. This "feature" is what you ran into and was causing the issue you observed.

As you are using the IEEE style the format is {first initials} {last name}. To change the order add (as of biblatex 3.3 [moewe]):

\DeclareNameAlias{default}{family-given}

to your preamble.

In versions prior to 3.3 this was:

\DeclareNameAlias{default}{first-last}

With the corrections that cslstr pointed out and the addition to your preamble:

\documentclass{article}
\usepackage[backend=bibtex, style=ieee]{biblatex}
\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@book{medianmean,
    author={Agresti, A. and Finlay, B.},
    title={Statistical Methods for the Social Sciences},
    publisher={Prentice Hall},
    edition={3},
    year={1997}
}

@article{DBLP:journals/corr/abs-cs-0703042,
    author    = {Brozovsky, L. and Petricek, V.},
    title     = {Recommender System for Online Dating Service},
    journal   = {CoRR},
    volume    = {abs/cs/0703042},
    year      = {2007},
    ee        = {http://arxiv.org/abs/cs/0703042},
    bibsource = {DBLP, http://dblp.uni-trier.de}
}
\end{filecontents}
\addbibresource{\jobname.bib}
\DeclareNameAlias{default}{family-given}

\begin{document}
\nocite{*}
\printbibliography[heading=bibnumbered]
\end{document}

will give you: