My suggestion would be to purchase it in small quantity, check for the quality of the product. I mean if it works for you and meet your requirements. Go for purchasing in bulk if you require so.
You have already received some answers from other RG colleagues, thus I would like only to add some additional information.
I don’t know what are the nanoparticles required by you, but I believe that you can consider some well-known suppliers of nanoparticles such as Skyspring Nanomaterials, Inc .( https://www.ssnano.com/ ), IoLiTec Nanomaterials (https://nanomaterials.iolitec.de/en), MKNano (https://www.mknano.com/ ), please consider the web site of Nanowerk for their base of data regarding the producers of nanomaterials (https://www.nanowerk.com/nanomaterial-database.php), etc.
Finally, the offer is very large and will be difficult for you to do the best choice.