A large number of revisions or iterations could mean that the client and the logo designer did not nail the creative brief BEFORE the start of the logo design process. You’re probably just running around in circles if the number of revisions and iterations on your logo design has exceeded ten. There are exceptions of course.
Depending on who you’re working with, you might get hand-drawn pencil sketches to start with. This is typically not considered an iteration / revision. Revisions usually start when the logo designer has converted the sketch you have chosen into a more final-looking file and has added color to it. In a typical situation, the logo designer will use colors and typeface as suggested by you in the creative brief. Revisions usually include changes to the typeface and the color and in some cases modification of the shape / symbol / graphic.
Modifications to the graphic can include making the shapes sharper or smoother, improving the shape of the curve, putting more / less distance between the graphic and the typeface and placement of the symbol / graphic with respect to placement of the typeface. Size ratios of the typeface and symbol / graphic can also be considered. These are changes that can be considered revisions or iterations.
Changing the entire sketch is not an iteration – that would be an additional logo option altogether. If this is done after the client has chosen a sketch from the set of sketches the logo designer provided, it would be done at an additional cost. This is because this usually means that the client has changed some element of the brief and a change in the brief means additional exploration and work, not within the scope of the original engagement.
Ideally, the logo designer will try and limit the number of options and iterations / revisions while giving you the pricing / proposal. This helps in establishing effort required, and hence the pricing for the logo design engagement.